cannot connect to the docker daemon at unix:///var/run/docker.sock. is the docker daemon running?

Cannot connect to the docker daemon at unix:///var/run/docker.sock. is the docker daemon running?

The above error is very common in docker as there any many factors that cause this and we will see the practical use cases of then and the explanation with solutions.

Firstly the socket file is the main Unix/Linux pipe that is used by the dockerd which provides a self-sufficient runtime environment for the docker containers.

We generally come across the issues with the following error stating "Docker: Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock” as the aprticular user executing docker cli is not authorized

We have a simple fix for this issue, As a Best practice on linux server running docker daemon, we need to update the following file /etc/sysconfig/docker with relevant docker group as shown below:

# /etc/sysconfig/docker

# Modify these options if you want to change the way the docker daemon runs
OPTIONS='--selinux-enabled --log-driver=journald --signature-verification=false -G dockerroot'

We have added the new Value of -G dockerroot to the OPTIONS= in /etc/sysconfig/docker
-G is the Flag to add the linux group and dockerroot is the privileged docker linux group for the docker daemon on centos/RHEL systems.
We now need to save the file and restart the docker daemon as we have modified the configuration file for the Docker daemon.

[vamshi@node01 ~]$ sudo systemctl restart docker

We now need to ensure the user accessing the docker command is part of the group dockerroot using usermod command as shown below.

[root@node01 ~]# sudo usermod -aG dockerroot vamshi

We now verify the user group information and verify the user is part of the group dockerroot.

[root@node01 ~]# id vamshi
uid=1001(vamshi) gid=1001(vamshi) groups=1001(vamshi),10(wheel),994(dockerroot)

You need relogin back if you are using the username to apply the linux group changes and once you login back you will be able to access the docker with the user account.

This process works for centos systems as we have modified the file /etc/sysconfig/docker and
The same approach can be implemented on Debian/Ubuntu systems by modifying /etc/default/docker which we will look at another post.

Now lets look at the second approach to the problem which is more of getting your hands dirty..
You will now modify the socket file by Hand as we will demonstrate in the following demonstration.

For us to be able to access this, we have to be have a read permission to this socket.
The permissions on /var/run/docker.sock will be as follows:

[vamshi@node02 ~]$ ls -l /var/run/docker.sock
srw-rw----. 1 root root 0 Apr 07 14:02 /var/run/docker.sock

As I mentioned earlier this being a socket file, as the symbol s is indicated at the start of the file permission attributes in the above output.

To overcome this issue, we have to create a docker group on the docker server as follows:

[vamshi@node02 ~]$ sudo groupadd docker

We check the group entity with the following command:

[vamshi@node02 ~]$ sudo getent group docker
docker:x:1009:

Now applying the docker group ownership to /var/run/docker.sock

[vamshi@node02 ~]$ sudo chgrp docker /var/run/docker.sock

And Here is the socket file attributes with updated group ownership:

[vamshi@node01 ~]$ ls -l /var/run/docker.sock 
srw-rw----. 1 root docker 0 Apr 07 14:09 /var/run/docker.sock

Now we have to add our user to the docker group to gain the rw permissions.
We do that in the following steps:

# sudo usermod -aG docker vamshi

Now we confirm the group members as below:

[vamshi@node02 ~]$ sudo getent group docker
docker:x:1009:vamshi

Now we need to logout and login back to this system and we will be able to access the docker command with the user.

The Other issues you might face while accessing the docker cli is probably accessing the docker server over a network where in the connection is established over the TCP connection with the docker server.

The docker server is also capable of handling the requests over the network provided it is exposed over a TCP port.
In most of the docker client server architecture, The Docker server listens on a tcp port over the network and This will be the second scenario where you have to access the docker server over the tcp socket and have to enable to the DOCKER_HOST with the docker server details over tcp.

You can try to connect to the docker server as follows

[user@docker-client ~]$ docker -H tcp://<Your-Docker-Server-IP>:<Port> version

Below is a practical command example:

[vamshi@jenkins-slave01 ~]$ docker -H tcp://10.100.0.10:4243 version

This scenario is most common with build agents like the jenkins slave and containers which run the post build and perform deployments. and is more common in the jenkins build environment..

The third most probable cause being that the actual docker server is not running if you have a local only setup and you can confirm by running the simple troubleshooting steps below by checking the process list and grep for docker process
ps -ef | grep docker and ensure that you have the docker services is started sudo systemctl status docker and ensure that its enabled on startup with sudo systemctl enable docker

Please refer our other Devops documents and do share your best practices in comments.

How do you fix Docker Cannot connect to the Docker daemon at Unix VAR run Docker sock is the Docker daemon running?

How to Resolve the “cannot connect to the Docker daemon” Error

  1. Method 1: Check the Docker Engine.
  2. Method 2: Assign Ownership to the Docker Unix Socket.
  3. Method 3: Check the Ownership of Used Files.
  4. Method 4: Add Your User to the Docker Group.
  5. Method 5: Add Environment Tables on OS X.

How do I connect to a Docker daemon?

How to Connect to a Remote Docker Daemon

  1. sudo mkdir -p /etc/systemd/system/docker.service.d.
  2. sudo nano /etc/systemd/system/docker.service.d/options.conf.
  3. [Service] ExecStart= ExecStart=/usr/bin/dockerd -H unix:// -H tcp://0.0.0.0:2375.
  4. # Reload the systemd daemon.

How do I make sure Docker daemon is running?

Another way to check for a running Docker daemon is by inspecting its process ID file. The daemon writes its process ID to /var/run/docker. pid each time it starts up. When this file exists, Docker should be running and ready for CLI connections.

Is the Docker daemon running Docker in Docker?

Docker daemon by default listens to docker. sock. If you are on the same host where Docker daemon is running, you can use the / var/run/docker. … To run docker inside docker, all you have to do it just run docker with the default Unix socket docker.

Is the Docker daemon running MacOS?

On macOS the docker binary is only a client and you cannot use it to run the docker daemon, because Docker daemon uses Linux-specific kernel features, therefore you can’t run Docker natively in OS X.

What is Unix VAR run?

A new TMPFS-mounted file system, /var/run , is the repository for temporary system files that are not needed across system reboots in this Solaris release and future releases. For security reasons, /var/run is owned by root.

What is Unix VAR run Docker sock?

sock is basically the Unix socket the Docker daemon listens on by default. It is also a tool used to communicate with the Docker daemon from within a container. The image shows how container can access the features of docker daemon without being part of the interface itself.

What is Docker daemon and Docker?

Docker Daemon is simply a part of Docker Engine. Quoting the Docker engine overview page: Docker Engine is an open source containerization technology for building and containerizing your applications. Docker Engine acts as a client-server application with: A server with a long-running daemon process dockerd.

What is Docker daemon?

Docker daemon is a persistent background process that manages the containers on a single host. It is a self-sufficient runtime that manages Docker objects such as images, containers, network, and storage. … By default, Docker daemon creates a non-networked Unix domain socket at /var/run/docker.

How do I shutdown a docker daemon?

To stop the docker process that is already running you can just press ctrl + c or send a kill signal to it.

Where is Docker daemon port?

Check your Docker daemon. After restarting docker service, you can see the port in the output of systemctl status docker. service like /usr/bin/dockerd -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock

Install java on Linux centos

In this tutorial we will quickly setup java on linux centos,

We will be using the yum command to download the openjdk 1.8 and install

[vamshi@node01 ~]$ sudo yum install java-1.8.0-openjdk.x86_64

We have installed the java openjdk 1.8 and we can check the version using java -version

[vamshi@node01 ~]$ java -version
openjdk version "1.8.0_252"
OpenJDK Runtime Environment (build 1.8.0_252-b09)
OpenJDK 64-Bit Server VM (build 25.252-b09, mixed mode)

 

We make use of the alternatives command in centos which lists if we have any other version of java installed on the machine, and then enabling the default java version on the system wide.

[vamshi@node01 ~]$ alternatives --list | grep java
java auto /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre/bin/java
jre_openjdk auto /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre
jre_1.8.0 auto /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre
jre_1.7.0 auto /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.261-2.6.22.2.el7_8.x86_64/jre
[vamshi@node01 ~]$ sudo alternatives --config java

There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
*  1           java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre/bin/java)
 + 2           java-1.7.0-openjdk.x86_64 (/usr/lib/jvm/java-1.7.0-openjdk-1.7.0.261-2.6.22.2.el7_8.x86_64/jre/bin/java)

Enter to keep the current selection[+], or type selection number: 1

This enabled openjdk1.8 to be the default version of java.

Setting JAVA_HOME path
In order to set the system JAVA_HOME path on the system we need to export this variable, for the obvious reasons of other programs and users using the classpath such as while using maven or a servlet container.

Now there are two levels we can setup the visibility of JAVA_HOME environment variable.
1. Setup JAVA_HOME for single user profile
We need to update the changes to the ~/.bash_profile

export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre/bin/

PATH=$PATH:$JAVA_HOME

export PATH

Now we need enforce the changes with reloading the .bash_profile with a simple logout and then login into the system or we can source the file ~/.bash_profile as follows:

[vamshi@node01 ~]$ source .bash_profile

Verifying the changes:

[vamshi@node01 ~]$ echo $PATH
/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/vamshi/.local/bin:/home/vamshi/bin:/home/vamshi/.local/bin:/home/vamshi/bin:/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre/bin/

2. Setup JAVA_HOME for the system wide profile and available to all the users.

[vamshi@node01 ~]$ sudo sh -c "echo -e 'export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre/bin/' > /etc/profile.d/java.sh"

This echo command writes the JAVA_HOME path to the system profile.d and creates a file java.sh which is read system wide level.

Ensure the changes are written to /etc/profile.d/java.sh

[vamshi@node01 ~]$ cat /etc/profile.d/java.sh
export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre/bin/

Now source to apply the changes immediately to the file /etc/profile.d/java.sh as follows

[vamshi@node01 ~]$ sudo sh -c ' source /etc/profile.d/java.sh '

Or login to the root account and run the source command

Ensure to run the env command

[vamshi@node01 ~]$ env  | grep JAVA_HOME
JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-2.el7_8.x86_64/jre/bin/

How do I download and install Java on CentOS?

Install Java On CentOS

  1. Install OpenJDK 11. Update the package repository to ensure you download the latest software: sudo yum update. …
  2. Install OpenJRE 11. Java Runtime Environment 11 (Open JRE 11) is a subset of OpenJDK. …
  3. Install Oracle Java 11. …
  4. Install JDK 8. …
  5. Install JRE 8. …
  6. Install Oracle Java 12.

Is Java installed on CentOS?

OpenJDK, the open-source implementation of the Java Platform, is the default Java development and runtime in CentOS 7. The installation is simple and straightforward.

How do I install Java on Linux?

  • Java for Linux Platforms
  • Change to the directory in which you want to install. Type: cd directory_path_name. …
  • Move the . tar. gz archive binary to the current directory.
  • Unpack the tarball and install Java. tar zxvf jre-8u73-linux-i586.tar.gz. The Java files are installed in a directory called jre1. …
  • Delete the . tar.

How do I install latest version of Java on CentOS?

To install OpenJDK 8 JRE using yum, run this command: sudo yum install java-1.8. 0-openjdk.

Where is java path on CentOS?

They usually reside in /usr/lib/jvm . You can list them via ll /usr/lib/jvm . The value you need to enter in the field JAVA_HOME in jenkins is /usr/lib/jvm/java-1.8.

How do I know if java is installed on CentOS 7?

  • To check the Java version on Linux Ubuntu/Debian/CentOS:
  • Open a terminal window.
  • Run the following command: java -version.
  • The output should display the version of the Java package installed on your system. In the example below, OpenJDK version 11 is installed.

Where is java path set in Linux?

Steps

  • Change to your home directory. cd $HOME.
  • Open the . bashrc file.
  • Add the following line to the file. Replace the JDK directory with the name of your java installation directory. export PATH=/usr/java/<JDK Directory>/bin:$PATH.
  • Save the file and exit. Use the source command to force Linux to reload the .

How do I install java 14 on Linux?

Installing OpenJDK 14

  • Step 1: Update APT. …
  • Step 2: Download and Install JDK Kit. …
  • Step 3: Check Installed JDK Framework. …
  • Step 4: Update Path to JDK (Optional) …
  • Step 6: Set Up Environment Variable. …
  • Step 7: Open Environment File. …
  • Step 8: Save Your Changes.

How do I know where java is installed on Linux?

This depends a bit from your package system … if the java command works, you can type readlink -f $(which java) to find the location of the java command. On the OpenSUSE system I’m on now it returns /usr/lib64/jvm/java-1.6. 0-openjdk-1.6. 0/jre/bin/java (but this is not a system which uses apt-get ).

How do I install java 11 on Linux?

Installing the 64-Bit JDK 11 on Linux Platforms

  1. Download the required file: For Linux x64 systems: jdk-11. interim. …
  2. Change the directory to the location where you want to install the JDK, then move the . tar. …
  3. Unpack the tarball and install the downloaded JDK: $ tar zxvf jdk-11. …
  4. Delete the . tar.

Bash Vs KSH

Bash Vs KSH

Linux and Unix have various shells. Two kinds of these numerous shells are KSH and BASH.

KSH (The Korn Shell) was developed many years before the BASH. Ksh has associative arrays and handles loop syntax better than bash. Also ksh’s command print is better than bash’s echo command. In other way, ksh does not support history completion, process substitution and rebindable command-line editing.

Bash has more added extension than ksh. Bash has tab completion and easier method to set a prompt in order to display current directory.

Compared to ksh, bash is newer and more popular.

Example of difference ksh and bash in condition test. First bash:

if [ $i -eq 3 ]

and condition test in ksh:

if (($i==3))

Bash can handle exit codes from pipes in a cleaner way. Bash and KSH are both Bourne=compatible shells, they share common functions and features and can be interchangeable to use.

Is ksh same as bash?

KSH and Bash shells are also products of combinations of other shells’ features. Bash and KSH are both Bourne-compatible shells. Since they share common features, they can be used interchangeably.

Is ksh faster than bash?

The ksh and zsh seems about seven times faster than bash . The ksh excelled in 17 tests and the zsh in six tests.

What is the difference between ksh CSH and bash?

CSH is C shell while BASH is Bourne Again shell. 2. C shell and BASH are both Unix and Linux shells. While CSH has its own features, BASH has incorporated the features of other shells including that of CSH with its own features which provides it with more features and makes it the most widely used command processor.

Is ksh a Linux shell?

Ksh is an acronym for KornSHell. It is a shell and programming language that executes commands read from a terminal or a file. It was developed by David Korn at AT&T Bell Laboratories in the early 1980s. It is backwards-compatible with the Bourne shell and includes many features of the C shell.

Why is ksh used?

ksh is a command and programming language that executes commands read from a terminal or a file. rksh is a restricted version of the command interpreter ksh; it is used to set up login names and execution environments whose capabilities are more controlled than those of the standard shell.

How do I run a ksh script in Bash?

How do I run . sh file shell script in Linux?

  • Open the Terminal application on Linux or Unix.
  • Create a new script file with .sh extension using a text editor.
  • Write the script file using nano script-name-here.sh.
  • Set execute permission on your script using chmod command : chmod +x script-name-here.sh.
    To run your script :

Is dash faster than Bash?

If you need speed, go definitely with dash, it is much faster than any other shell and about 4x faster than bash.

What is faster than Bash?

Perl is absurdly faster than Bash. And, for text manipulation, you can actually achieve better performances with Perl than with C, unless you take time to write complex algorithms.

How much faster is dash than Bash?

Dash is not Bash compatible, but Bash tries to be mostly compatible with POSIX, and thus Dash. Dash shines in: Speed of execution. Roughly 4x times faster than Bash and others.

What is difference between sh and ksh in Unix?

sh is the original Bourne shell. On many non-Linux systems, this is an old shell without the POSIX features. Thus bash and ksh (or even csh and tcsh) are better choices than sh. … Public domain ksh (pdksh) is Bourne-compatible and mostly POSIX-compatible.

Is zsh better than Bash?

It has many features like Bash but some features of Zsh make it better and improved than Bash, such as spelling correction, cd automation, better theme, and plugin support, etc. Linux users don’t need to install the Bash shell because it is installed by default with Linux distribution.

Linux Commands Cheat Sheet

Do you want to learn the Linux commands? If yes, then you are in the right place. There are uncountable commands in Linux. Generally, we use some of the Linux commands from the Linux commands cheat sheet regularly to perform the common tasks.

pythonarray.com is a free Python tutorial website for people who want to learn Python, fast.

You can also learn Google Sheets Tips – New Google Spreadsheet Hacks, Tricks with Examples

Types of Linux Commands

All the Linux commands are categorized into 7 different types. They are Basic Linux commands, File permission commands, Environment variables commands, User management commands, Networking commands, Process commands, VI Editing commands, Other Commands.

We are giving a detailed explanation for each and every Linux command with their examples for easy learning in the below sections. Have a look at them and follow them. Check the actual description of each Linux command in their manual page.

Basic Linux Commands

  • ls command:

It is used to list all files and directories of a directory. The ‘-l’ option gives the long listing format. Its syntax is $ ls [options] [file|dir]

Example: $ ls -l samplefile

  • ls-R command:

It gives the lists files in subdirectories. List recursively directory tree and syntax is $ ls -R [options] [file|dir]

Example: $ ls -R samplefile

  • ls -a Command:

It lists all files including hidden files starting with’.’ Its syntax is $ ls -a [options] [file|dir]

  • ls -al Command:

It lists all files details and directories with detailed information like permissions, size, owner, etc. Syntax is $ ls -al [options] [file|dir]

  • cd or cd ~ Command:

This command will navigate to the home directory or change the directory. Its syntax is $ cd [directory]

Example: $ cd Directory1

  • cd .. Command:

It moves one level up. Syntax is $ cd . . [directory]

  • cd Command:

Use this command to change to a particular directory. Its syntax is $ cd [directory]

Example: $ cd directory1

  • cd / Command:

This command will move to the root directory. Syntax is $ cd /

  • cat filename Command:

Create a new file using this command in Linux. Its syntax is $ cat filename.

Example: $ cat filename1

  • cat filename Command:

It displays the content in that particular file. The syntax is $ cat filename.

Example: $ cat filename1.

  • cat file1 file2 file3 Command:

It combines two files namely file1 and file2 and stores the output in a new file called file3. Its syntax is $ cat file1 file2 file3.

Example: $ cat add multiply arithmetic.

  • mv file “new file path” Command:

It moves the files to the new location. Syntax is $ mv file “new file path”.

Example: $ mv add “E:/Arithmeticopeartions/”.

  • mv filename new_file_name Command:

It renames or changes the file name to a new file name. Syntax is $ mv filename new_file_name.

Example: $ mv add sum

  • sudo Command:

sudo command allows a permitted user to run a command as root or another user. It runs commands in superuser mode. The syntax is $ sudo filename option

Example: $ sudo apt update

  • rm Command:

It is used to remove the files or directories. Syntax is $ rm filename or $ rm directory

Examples: $ rm sum and $ rm mydrive

  • man Command:

It is used to view the online reference manual pages for the commands or programs. It provides the help information of any commands. Its syntax is $ man commandname

Example: $ man cd

  • history Command:

It produces the list of previously used commands and gets the all past commands types in the current terminal session. The syntax is $ history

  • clear Command:

clear command is helpful to clear the terminal screen. The syntax is $ clear

  • mkdir directoryname Command:

It creates a new directory in the present working directory or at any specific path. Syntax is $ mkdir directoryname

Example: $ mkdir new_directory

$ mkdir -p new_directory: Here -p option is used to override the already available directory.

  • rmdir Command:

It helps to remove/ delete the empty directories. Syntax is $ rmdir [directory_name]

Example: $ rmdir new_directory

  • mv Command:

It is helpful to rename files or directories. mv command also moves a file or a directory to another location in the directory structure. Its syntax is $ mv file1 file2

Example: $ mv add sum

  • pr -x Command:

It divides the file into x columns. Syntax is $ pr -x filename.

Example: $ pr -5 add

  • pr -h Command:

It is useful to assign a header to the file. Syntax is $ pr -h filename

Example: $ pr -h sum

  • pr -n Command:

This command denotes the file with the line numbers. Its syntax is $ pr -n file

Example: $ pr -n sum

  • lp -nc , lpr c Command:

It prints the c number of copies of a file. lp stands for a line printer. Its syntax is $ lpr c filename

Example: $ lpr 5 sum

  • lp -d lp -P Command:

It specifies the name of the printer. The syntax is $ lp -P

  • apt-get Command:

It is a powerful and free front end package manager for Debian/Ubuntu systems. It is used to install new software packages, remove available software packages, upgrade existing software packages, and upgrade the entire operating system. Its syntax is $ apt-get package

Example: $ sudo apt-get update

  • mail -s ‘subject’ -c ‘cc-address’ -b ‘bcc-address’ ‘to-address’ Command:

It is a linux command used to send mail. Syntax is $ mail -s ‘subject’ -c ‘cc-address’ -b ‘bcc-address’ ‘to-address’

Example: $ mail -s ‘regarding_job’ -c ‘add@gmail.com’ -b ‘sum@gmail.com’ ‘arithmetic@gmail.com’

  • mail -s “Subject” to-address < Filename Command:

It is used to send an email with an attachment. Its syntax is $ mail -s “Subject” to-address < Filename

Example: $ mail -s “Addition of Numbers” sum@gmail.com < Addition

File Permission Commands

  • ls-l Command:

Use this command to show file type and access permission of any particular file. Syntax is $ ls-l filename

Example: $ ls-l sum

  • r Command:

It is used to give read permission to a file. The syntax is $ r filename.

Example: $ r sum

  • w Command:

It gives write permission to the file. The syntax is $ w filename

Example: $ w sum

  • x Command:

It is useful to provide execute permission to the file. Its syntax is $ x filename

Example: $ x sum

  • -= Command:

This command is used when you want to give no permission to a file. Syntax is $ -= filename

Example: $ -= file1

  • Chown user Command:

It is helpful to change the ownership of a file/directory. The syntax is $ chown user filename

Example: $ chown user file1

  • Chown user:group filename Command:

It changes the user and group for a file or directory. Syntax is $ chown user:group filename

Example: $ chown user:group sum

Environment Variables Command

  • echo $VARIABLE Command:

It displays the value of a variable or prints a text of the line. Its syntax is echo [option] [string]

Example: $ echo “Print this line” or $ echo $VARIABLE var1

  • env Command:

It lists all environment variables. The syntax is $ env

  • VARIABLE_NAME= variable_value Command:

It creates a new variable and assigns it a value. Syntax is $ VARIABLE_NAME= variable_value

Example: $ My_Variable= 10

  • Unset Command:

It removes a variable. Syntax is $ Unset VARIABLE_NAME

Example: $ Unset My_Variable

  • export Variable=value Command:

It is helpful to set the value of an environment variable. Syntax is $ export Variable=value

Example: $ export Variable1=90

User Management Commands of Linux

  • sudo adduser username Command:

It is used to create a username. The syntax is $ sudo adduser username

Example: $ sudo dduser user1

  • sudo passwd -l ‘username’ Command:

It is helpful to change the user password. Syntax is $ sudo passwd -l ‘username’

Example: $ sudo passwd -l ‘user1’

  • sudo userdel -r ‘username’ Command:

This command is used to add and delete users on Linux. Syntax is $ sudo userdel -r ‘username’

Example: $ sudo userdel -r ‘user1’

  • finger Command:

It is a user information lookup command which provides details of all users logged in. The Syntax $ finger

  • finger username Command:

It gives the login details of that particular user. Syntax $ finger username

Example: $ finger user1

Networking Commands

  • SSH username@ip-address or hostname Command:

You can log in to a remote Linux machine using SSH. The syntax is $ SSH username@ip-address or hostname

Example: $ SSH user1@https:11//1001

  • Ping hostname=”” or =”” Command:

It is used for analyzing the network and host connections. Syntax is $ Ping hostname=”” or =””

Example: $ Ping hostname=”host1″

  • dir Command:

It displays all files in the current directory of a remote computer. The syntax is $ dir

  • cd “dirname” Command:

It changes the current directory to “dirname” on a remote computer. Syntax is $ cd “dirname”

Example: $ cd “E”

  • put file Command:

It is helpful to upload the file from local to the remote computer. The syntax is $ put file

Example: $ put sum

  • get file Command:

It is used to download the file from remote to the local computer. The syntax is $ get file

Example: $ get add

  • quit Command:

It is used to logout from that network. The syntax is $ quit

Process Commands

  • bg Command:

You can send a process to the background with this command. The syntax is $ bg processname

Example: $ bg process1

  • fg Command:

To run a stopped process in the foreground. The syntax is $ fg processname.

Example: $ fg process1

  • top Command:

It gives the details of all active processes in the directory. The syntax is $ top

  • ps Command:

It produces the status of processes running for a user. The syntax is $ ps username

Example: $ ps user1

  • ps PID Command:

This command gives the status of a particular process. The syntax is $ ps PID processname

Example: $ ps PID process1

  • pidof Command:

It gives the process id of a process. The syntax is $ pidof processname.

Example: $ pidof process1

  • kill PID Command:

It kills a process. The syntax is $ kill PID processname

Example: $ kill PID process1

  • nice Command:

It is used to start a process with the given priority. The syntax is $ nice processname.

Example: $ nice process

  • renice Command:

It is used to change the priority of an already running process. The syntax is $ renice processname

Example: $ renice process2

  • df Command:

It provides free hard disk space on your system. The syntax is $ df

  • free Command:

It gives free RAM space on your system. The syntax is $ free

VI Editing Commands

  • i Command:

It inserts at the cursor i.e goes to insert mode. The syntax is $ i

  • a Command:

It is used to write after the cursor in insert mode. The syntax is $ a

  • A Command:

This command is used to write at the end of the line in insert mode. The syntax is $ A

  • ESC Command:

It is helpful to terminate insert mode. The syntax is $ ESC.

  • u Command:

It undoes the last change. The syntax is $ u.

  • U Command:

It undoes all changes to the entire line. The syntax is $ U

  • o Command:

It opens a new line in insert mode. The syntax is $ o

  • dd Command:

It deletes that particular line. The syntax is $ dd line number

Example: $ dd 25

  • 3dd Command:

This command deletes 3 lines. The syntax is $ 3dd line number

Example: $ 3dd 25

  • D Command:

It deletes the contents of a line after the cursor. The syntax is $ D

  • C Command:

It is used to delete the contents of a line after the cursor and insert new text. Press the ESC key to end the insertion. Syntax is $ C

  • dw Command:

Delete a word using this command. The syntax is $ dw

  • 4dw Command:

It is used to delete 4 words. The syntax is $ 4dw

  • cw Command:

It is used to change a word. Syntax is $ cw

  • x Command:

It deletes the character at the cursor. Syntax is $ x

  • r Command:

Replace the character. The syntax is $ r

  • R Command:

It overwrites characters from cursor onward. The syntax is $ R

  • s Command:

Substitute one character under the cursor and continue to insert. The syntax is $ s

  • S Command:

Substitutes the entire line and starts to insert at the beginning of the line. The syntax is $ S

  • ~ Command:

It is used to change the case of the individual character. Syntax is $ ~

Other Linux Commands

  • adduser/addgroup Command:

adduser adds a user and addgroup adds groups to the system. The syntax is $ adduser username

Example: $ sudo adduser tech

  • agetty Command:

agetty is a program that manages physical or virtual terminals and is invoked by init. It is the substitute for Linux getty.

Example: $ agetty -L 9600 ttyS1 vt100

  • alias Command:

It is a useful shell built-in command for creating shortcuts to a Linux command on a system.

Example: $ alias home’cd /home/drive/file1′

  • apropos Command:

This is used to search and display a short man page description of a program/ command. The syntax is $ apropos commandname

Example: $ apropos rm

  • aptitude Command:

It is a powerful text-based interface to the Debian Linux/GNU package management system. The syntax is $ aptitude package

Example: $ sudo aptitude update

  • arch Command:

This command is used to display the machine architecture or hardware name. The syntax is $ arch

  • arp Command:

ARP stands for Address Resolution Protocol that maps IP network addresses of a network neighbor with the hardware (MAC) addresses in an IPv4 network.

Example: $ sudo arp-scan –interface=enp2s0 –localnet

  • at Command:

It is used to schedule tasks to run in the forthcoming time. Syntax is $ at

Example: $ sudo echo “shutdown -h now” | at -m 15:20

  • atq Command:

This command is used to view jobs in at command queue. Syntax is $ atq

  • atrm Command:

It is helpful to delete/remove jobs from the queue. $ atrm 2

  • awk Command:

Awk is a programming language created for text processing and used as a data extraction and reporting tool.

Example: $ awk ‘//{print}’/etc/hosts

  • batch Command:

It is similar to at command which is useful to schedule tasks to run in a future time. Syntax is $ batch

  • basename Command:

It helps to print the name of a file stripping of directories in absolute path. Syntax is $ basename filename

Example: $ basename samplefile

  • bzip2 Command:

It is useful to compress or decompress the files. Syntax is $ bzip2 filename

Example: $ bzip2 -z filename #Compress

$ bzip2 -d filename.bz2 #Decompress

  • cal Command:

This command is used to print a calendar on the standard output. Syntax is $ cal

  • chgrp Command:

It is used to change the group ownership of a file. Syntax is $ chgrp new_group_name filename

Example: $ chgrp Product Multiplication.txt

  • chmod Command:

It is used to change/ update file access permissions. Syntax is $ chmod permission filename

Example: $ chmod +x product.txt

  • cksum Command:

This command is used to provide the checksum and byte count of the given input file. Syntax is $ cksum filename

Example: $ cksum product.txt

  • cmp Command:

It compares byte by byte comparison of two files. Syntax is $ cmp file1 file2

Example: $ cmp sum add

  • comm Command:

It is used to compare two sorted files line by line. Syntax is $ comm file1 file2

Example: $ comm product multiplication

  • cp Command:

It copies files and directories from one location to another. Syntax is $ cp location1 location2

Example: $ cp /home/arithmetic/add /home/arithmetic/product/

  • date Command:

It displays/ sets the system date and time. Syntax is $ date

Example: $ date –set=”20 Oct 2020 10:35:05″

  • diff Command:

The double advantage of this command is used to compare two files line by line and used to find the difference between two directories. Syntax is $ diff file1 file2

Example: $ diff sum add

  • dmidecode Command:

It retrieves the hardware information of any linux system. Syntax is $ dmidecode

Example: $ sudo dmidecode –type system

  • du Command:

It shows the disk space usage of files present in the directory as well as its subdirectories. The syntax is $ du directory

Example: $ du /home/arithmetic

  • eject Command:

eject command is used to eject removable media such as CD/DVD/ROM/floppy disk from the system. The syntax is $ eject disklocation

Example: $ eject /dev/cdrom

  • exit Command:

It is used to exit a shell. The syntax is $ exit

  • expr Command:

It is used to calculate an expression. The syntax is $ expr expression

Example: $ expr 15 * 5

  • factor Command:

It is used to display the prime factors of a number. The syntax is $ factor number

Example: $ factor 18

  • find Command:

It searches for files in the directory and its subdirectories. The syntax is $ find directory filename

Example: $ find /home/add/ -name product.txt

  • grep Command:

It searches for a specified pattern in the file and displays the output as lines containing that pattern. The syntax is $ grep

Example: $ grep ‘linuxcent’ domain-list.txt

  • groups Command:

Shows all names of groups of a user. The syntax is $ groups

  • gzip Command:

It helps to compress a file and replaces it with one having a .gz extension. The syntax is gzip filename

Example: $ gzip passwds.txt

  • gunzip Command:

It expands or restores files compressed with the gzip command. The syntax is $ gunzip gzfilename

Example: $ gunzip sum.gz

  • head Command:

It is helpful to display the first 10 lines of the specified file or stdin to the screen. The syntax is $ head

  • hostname Command:

This command is useful to print or set the system hostname. The syntax is $ hostname

Example: $ hostname New_hostname

  • id Command:

It shows user & group information for the current user or specified user. The syntax is $ id username

Example: $ id linuxcent

  • ifconfig Command:

It is used to configure Linux system network interfaces. The syntax is $ ifconfig

  • ionice Command:

This command is used to set or view process I/O scheduling class and priority of the specified process. The syntax is $ ionice process

Example: $ ionice -c 3 rm /var/logs/syslog

  • iostat Command:

iostat command is helpful to show the CPU and i/o statistics for devices and partitions. The syntax is $ iostat

  • ip Command:

It is used to display or manage devices, routing, policy routing, and tunnels. The syntax is $ ip addr

  • iw Command:

This is used to manage wireless devices and their configuration. The syntax is $ iw

Example: $ iw list

  • killall Command:

It kills a process with the help of its name. The syntax is $ killall processname

Example: $ killall process1

  • kmod Command:

It is useful to manage Linux kernel modules. To list all currently loaded modules, type. Syntax is $ kmod

Example: $ kmod list

  • last Command:

It displays a list of last logged in users. The syntax is $ last

  • ln Command:

This is used to create a soft link between files using -s flag. Syntax is $ ln -s file1 file2

Example: $ ln -s product multiplication

  • locate Command:

It is used to find a file with its name. The syntax is $ locate filename

Example: $ locate -b ‘add.txt’

  • lshw Command:

It gives detailed information on the hardware configuration of the machine. The syntax is $ lshw

  • lscpu Command:

This Linux command displays the system’s CPU architecture information. The syntax is $ lscpu

  • lsof Command:

It displays information related to files opened by processes. The syntax is $ lsof processname

Example: $ lsof -u add

  • lsusb Command:

It shows information: about USB buses in the system and devices connected to them. The syntax is $ lsusb

  • md5sum Command:

This command is used to compute and print the MD5 message digest of the file.

  • more Command:

It enables to view through relatively lengthy text files one screenful at a time. The syntax is $ more filename

Example: $ more add

  • nano Command:

You can open a file using this nano command. The syntax is $ nano filename

Example: $ nano sum

  • netstat Command:

It displays useful information such as routing tables, network connections, and others about Linux networking subsystems. Syntax is $ netstat

Example: $ netstat -a | more

  • nproc Command:

It shows the number of processing units present to the current process. The syntax is $ nproc

  • passwd Command:

This command is used to create/update passwords for user accounts. The syntax is $ passwd username

Example: $ passwd user1

  • pstree Command:

It displays running processes as a tree that is rooted at either PID or init if PID is omitted. The syntax is $ pstree

  • reboot Command:

This command is used to power-off, halt, or reboot a system. The syntax is $ reboot

  • scp Command:

It enables you to securely copy files between hosts on a network. Syntax is $ scp

Example: $ scp ~/names.txt root@192.168.56.10:/root/names.txt

  • shutdown Command:

It schedules a time for the system to be powered down. Its syntax is $ shutdown

Example: $ shutdown –poweroff

  • sleep Command:

This command is used to pause or delay for a specific amount of time. The syntax is $ sleep

Example: $ check.sh; sleep 5; sudo apt update

  • sort Command:

This is used to sort lines of text in the specified files from stdin. The syntax is $ sort

Example: $ sort add.txt

  • split Command:

It is used to split a large file into smaller pieces. The syntax is $ split filename

Example: $ split add

  • stat Command:

It is helpful to know the file system status. The syntax is $ state filename

Example: $ stat -f add.txt

  • su Command:

It is used to switch to another user ID or become root during a login session. The syntax is $ su

  • sum Command:

This command shows the checksum and blocks counts for all files on the command line. The syntax is $ sum output filename

Example: $ sum output add.txt

  • tac Command:

It concentrates and displays files in reverse. It prints each file to the standard output, shows the last line first. The syntax is $ tac filename

Example: $ tac sum.txt

  • tail Command:

It displays the last 10 lines of each file. The syntax is $ tail filename

Example: $ tail sum.txt

  • talk Command:

talk is used to talk to another network user/ system. Use a login name to talk to the user on the same machine and use ‘use@host’ to talk to a user on another machine. The syntax is $ talk

Example: $ talk person [ttyname] or $ talk ‘user@host’ [ttyname]

  • tee Command:

This is used to read from standard input & prints to standard output and files.

Example: $ echo “Testing how tee command works” | tee file1

  • time Command:

This command runs programs and summarizes system resource usage. The syntax is $ time

  • touch Command:

It changes file timestamps and it is used to create a file. The syntax is $ touch filename

  • uname Command:

It displays system information such as operating system, network node hostname kernel name, version, and release, etc. Syntax is $ uname

  • uniq Command:

It displays or omits repeated lines from input. The syntax is $ uniq

  • uptime Command:

It shows how long the system has been running, the number of logged on users, and system load averages. The syntax is $ uptime

  • wall Command:

This command is used to send/display a message to all users on the system. The syntax is $ wall “message”

Example: $ wall “This is Linux operating system”

  • wc Command:

This command displays the word, newline, and byte counts for each file. The syntax is $ wc filename

Example: $ wc add.txt

  • whatis Command:

It searches & shows a short or one-line manual page description of the provided command name. The syntax is $ whatis wget

  • who Command:

It shows details about users who are currently logged in. The syntax is $ who

  • which Command:

This command is used to get the absolute path of the file which would be executed in the current environment. The syntax is $ which who

  • whereis Command:

It helps to locate binary, source and manual files for commands. The syntax is $ whereis cat

  • yes Command:

This command is used to display a string repeatedly until when terminated or killed. The syntax is 4 yes

Example: $ yes “This is LinuxCent – Linux HowTos”

  • zcmp/zdiff Command:

zcmp and zdiff minimal utilities used to compare compressed files. Syntax is $ zcmp filesnames, $ zdiff filesnames

Example: $ zcmp domain-list.txt.zip basic_passwords.txt.zip

$ zdiff domain-list.txt.zip basic_passwords.txt.zip

  • zip Command:

It is simple & easy to use utility used to package & compress files. Syntax is $ zip packagename

Example: $ zip inarchive.zip foo.c bar.c –out outarchive.zip

We have mentioned all the Linux commands in the Linux Commands Cheatsheet. Make use of these countless commands that you might feel helpful.

What are 5 Linux commands?

Linux File commands

  • touch Command. The touch command is used to create empty files. …
  • cat Command. The cat command is a multi-purpose utility in the Linux system. …
  • rm Command. The rm command is used to remove a file.
  • cp Command. The cp command is used to copy a file or directory.
  • mv Command. …
  • rename Command.

How do I see all commands in Linux?

In Linux, there is a very useful command to show you all of the last commands that have been recently used. The command is simply called history, but can also be accessed by looking at your . bash_history in your home folder. By default, the history command will show you the last five hundred commands you have entered.

What is Linux cheat sheet?
Basic Linux commands

What is Linux cheat sheet?

How many commands are in Linux?

There are well over 100 Unix commands shared by the Linux kernel and other Unix-like operating systems.

What does F do in Linux?

Many Linux commands have an -f option, which stands for, you guessed it, force! Sometimes when you execute a command, it fails or prompts you for additional input. This may be an effort to protect the files you are trying to change or inform the user that a device is busy or a file already exists.

How do I get a list of commands?

You can open the Command Prompt by pressing ⊞ Win + R to open the Run box and typing cmd. Windows 8 users can also press ⊞ Win + X and select Command Prompt from the menu. Retrieve the list of commands.

How do you list all commands in Terminal?

Just tap the Tab key twice ( Tab Tab ). You’ll be prompted if you want to see all possible commands. Tap y and you’ll be presented with a list. You can do that same thing for individual commands to see all options for that specific command.

How do you write commands in Linux?

Linux operating system allows users to create commands and execute them over the command line. To create a command in Linux, the first step is to create a bash script for the command. The second step is to make the command executable. Here, bashrc means run the Bash file.

What does Linux dd command do?

dd is a command-line utility for Unix and Unix-like operating systems, the primary purpose of which is to convert and copy files. … As a result, dd can be used for tasks such as backing up the boot sector of a hard drive, and obtaining a fixed amount of random data.

What is Yum in Linux?

YUM is the primary package management tool for installing, updating, removing, and managing software packages in Red Hat Enterprise Linux. YUM performs dependency resolution when installing, updating, and removing software packages. YUM can manage packages from installed repositories in the system or from

What is Sudo in Linux?

Sudo stands for either “substitute user do” or “super user do” and it allows you to elevate your current user account to have root privileges temporarily. This is different from “su” which is not temporary.

How use Linux command line?

On many systems, you can open a command window by pressing the Ctrl+Alt+t keys at the same time. You will also find yourself on the command line if you log into a Linux system using a tool like PuTTY. Once you get your command line window, you’ll find yourself sitting at a prompt.

What is Ubuntu command?

The latest LTS release is 20.04; it will be available till 2025. Ubuntu supports both Command Line Interface (CLI) and Graphical User Interface (GUI) to perform various tasks on the OS. CLI is the basic way to interact with systems hardware (processor/memory); you can perform all the tasks that GUI can perform.

Where is Linux command?

The whereis command in Linux is used to locate the binary, source, and manual page files for a command. This command searches for files in a restricted set of locations (binary file directories, man page directories, and library directories).

Git config setup on linux; Unable to pull or clone from git; fatal: unable to access git; Peer’s Certificate has expired

Facing an issue with pulling the repository while dealing with an expired SSL certificate.

[vamshi@workstation ~]$ git pull https://gitlab.linuxcent.com/linuxcent/pipeline-101.git
fatal: unable to access 'https://gitlab.linuxcent.com/linuxcent/pipeline-101.git/': Peer's Certificate has expired.
[vamshi@workstation ~]$

SSL error while cloning git URL

If you have faced the error, then we can work around it by ignoring SSL certificate check and continue working with the git repo.

[vamshi@workstation ~]$ git clone https://gitlab.linuxcent.com/linuxcent/pipeline-101.git
Cloning into 'pipeline-101'...
fatal: unable to access 'https://gitlab.linuxcent.com/linuxcent/pipeline-101.git/': Peer's Certificate has expired.

It doesn’t allow the clone or pull or push to the gitlab website as its certificate is not valid, and the certificate is unsigned by a Valid CA. In most cases, we will have the corporate gitlab repo in our internal network and not publicly exposed.
We therefore trust the gitlab server as we have a bunch of our code on it.. Why not, I say?
We have to ensure to disable the check for the SSL certificate verification

Set the Variable GIT_SSL_NO_VERIFY=1 or GIT_SSL_NO_VERIFY=false and try to execute your previous command.

[vamshi@workstation ~]$ GIT_SSL_NO_VERIFY=1 git clone https://gitlab.linuxcent.com/linuxcent/pipeline-101.git
Cloning into 'pipeline-101'...
Username for 'https://gitlab.linuxcent.com': vamshi
Password for 'https://vamshi@gitlab.linuxcent.com': 
remote: Enumerating objects: 3, done.
remote: Counting objects: 100% (3/3), done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.

Make a permanent entry to system wide user level profiles as below. The following change works at the system level

[vamshi@workstation ~]$ sudo bash -c "echo -e export GIT_SSL_NO_VERIFY=1 > /etc/profile.d/gitconfig.sh "
[vamshi@workstation ~]$ cat /etc/profile.d/gitconfig.sh
export GIT_SSL_NO_VERIFY=false

The practical use case of setting the environment variable can be made while building container images, using  the GIT_SSL_NO_VERIFY false as an environment variable in Dockerfile and building an image.

[vamshi@workstation ~]$ cat Dockerfile
FROM jetty:latest
-- CONTENT TRUNCATED --
env GIT_SSL_NO_VERIFY 1
-- CONTENT TRUNCATED --

We can also setup the container build agent with Jenkins Pipeline code with similar configuration to fetch a gitrepo in our next sessions.

Why is git clone not working?

If you have a problem cloning a repository, or using it once it has been created, check the following: Make sure that the path in the git clone call is correct. … If you have an authorization error, have an administrator check the ACLs in Administration > Repositories > <repoName> > Access.

How do I fix fatal unable to access?

How to resolve “git pull,fatal: unable to access ‘https://github.com… \’: Empty reply from server”

  1. If you have configured your proxy for a VPN, you need to login to your VPN to use the proxy.
  2. to use it outside the VPN use the unset command: git config –global –unset http.proxy.

How do I bypass SSL certificate in git?

Prepend GIT_SSL_NO_VERIFY=true before every git command run to skip SSL verification. This is particularly useful if you haven’t checked out the repository yet. Run git config http. sslVerify false to disable SSL verification if you’re working with a checked out repository already.

How do I open a cloned git repository?

Clone Your Github Repository

  • Open Git Bash. If Git is not already installed, it is super simple. …
  • Go to the current directory where you want the cloned directory to be added. …
  • Go to the page of the repository that you want to clone.
  • Click on “Clone or download” and copy the URL.

Can not clone from GitHub?

If you’re unable to clone a repository, check that:
You can connect using HTTPS. For more information, see “HTTPS cloning errors.”
You have permission to access the repository you want to clone. For more information, see “Error: Repository not found.”
The default branch you want to clone still exists.

Do I need git for GitLab?

To install GitLab on a Linux server, you first need Git software. We explain how to install Git on a server in our Git tutorial. Next, you should download the GitLab omnibus package from the official GitLab website.

How do I clone a project from GitHub?

Cloning a repository

  • In the File menu, click Clone Repository.
  • Click the tab that corresponds to the location of the repository you want to clone. …
  • Choose the repository you want to clone from the list.
  • Click Choose… and navigate to a local path where you want to clone the repository.
  • Click Clone.

How do I push code to GitHub?

Using Command line to PUSH to GitHub

  • Creating a new repository. …
  • Open your Git Bash. …
  • Create your local project in your desktop directed towards a current working directory. …
  • Initialize the git repository. …
  • Add the file to the new local repository. …
  • Commit the files staged in your local repository by writing a commit message.

Docker ADD vs COPY statement

The contents of the docker container image are created using personalized build artifacts and the configuration code which is copied from the build workspace during the docker build process, To achieve this purpose we use certain Docker DSL statements like ADD, COPY to dump the content to the docker image during the build process

It is good to throw some light into understanding the subtle differences between these statements.

It is important to send the up to date content to the Dockerfile and perform the build successfully, Lets see some practical case study of the Docker ADD vs COPY commands below:

Docker ADD statement

Docker COPY statement

Syntax:

ADD </host/Relative/path/to/source/> <Container/image/path/to/Destination/>
ADD [ "/host/path/source1/","/host/path/source2",.. "/container/path/target/" ]
Syntax:

COPY </host/Relative/path/to/source/> <container/image/path/to/Destination/>
COPY ["/host/path/source1/","/host/path/source2/",.. "/container/path/target/"  ]
ADD [source1,source2],,. /path/to/dest/

With multiple source files, the target container path must end with a /

COPY [source1,source2],,. /path/to/dest/

With multiple source files, the target container path must end with a /

The Destination path inside container image can be Absolute or Relative to WORKDIR The Destination path inside container image can be Absolute or Relative to WORKDIR
The Destination path will be automatically created on target container with 0755 permissions The Destination path will be automatically created on target container with 0755 permissions
ADD default.conf /tmp/default.conf

Creates the new files with the default 0644 permission

COPY default.conf /tmp/default.conf

Creates the new files with the default 0644 permission

The Destination content will be owned by the root user and the root group with uid & gid as 0 The Destination content will be owned by the root user and the root group with uid & gid as 0
ADD directory /app
COPY directory /app
ADD Directory Explanation: The whole directory will be copied from the source host to target container with directory permission as 0755 COPY Directory Explanation: The whole directory will be copied from the source host to target container with directory permission as 0755
ADD Portal.tar.gz /tmp/portal1/
COPY Portal.tar.gz /tmp/portal2/
Add Compressed file Explanation: The ADD command will extract the tar file and the extracted will be placed at the target container, with directory permissions as 0755 COPY Compressed file Explanation: The COPY command will NOT extract the tar files and places them as it is.. at the destination target container path as a single compressed tar file.
URL file as Source:

ADD https://ftp.gnu.org/gnu/wget/wget-1.6.tar.gz.sig /tmp/test-add/
URL file as Source – Not possible with COPY command

Source can't be a URL for COPY
ADD URL Explanation: With ADD the URL download and archive unpacking features cannot be used together Meaning it will be not extract the compressed tar.bz2 or tar.gz formats when it downloads from a URL inside the target container path. But it works just like RUN wget command and downloads the compressed package. Explanation:
COPY command will not be able treat source as a URL and Hence its not a valid command

 

Conclusion:
It is better to use ADD command if you have the source archive files like tar.gz, tar.bz2 and want to send them into your container image and extract them, ADD command does it automatically whilst the COPY command sends it as it is at source.

Both the ADD and COPY commands cannot access the source content which are outside of its current relative context path.
Eg:

ADD ../source-code /data
COPY ../source-code /data

You should always keep this in mind whilst writing Docker files.

Feel free to comment and share your experiences with the COPY / ADD commands.

Whats the difference between ADD and COPY Docker?

COPY only supports the basic copying of local files into the container, while ADD has some features (like local-only tar extraction and remote URL support) that are not immediately obvious. Consequently, the best use for ADD is local tar file auto-extraction into the image, as in ADD rootfs. tar.

What is the difference between COPY and add?

COPY copies a file/directory from your host to your image. ADD copies a file/directory from your host to your image, but can also fetch remote URLs, extract TAR files, etc

What is Docker add?

The ADD command is used to copy files/directories into a Docker image. It can copy data in three ways: Copy files from the local storage to a destination in the Docker image. Copy a tarball from the local storage and extract it automatically inside a destination in the Docker image.

What does COPY mean in Docker?

Dockerfiles can contain several different instructions, one of which is COPY. The COPY instruction lets us copy a file (or files) from the host system into the image. This means the files become a part of every container that is created from that image.

When should I use Docker COPY?

If you are copying local files to your Docker image, always use COPY because it’s more explicit. While functionality is similar, the ADD directive is more powerful in two ways: It can handle remote URLs. It can also auto-extract tar files.

Is Docker a recursive COPY?

Docker provides two commands for copying files from the host to the Docker image when building it: COPY and ADD . … COPY — copies local files recursively, given explicit source and destination files or directories.

Does Docker COPY overwrite?

It seems that docker build won’t overwrite a file it has previously copied. I have a dockerfile with several copy instructions, and files touched in earlier COPY directives don’t get overwritten by later ones.

How do I COPY a Docker container?

Solution

  1. To copy a file from the local file system to a container, run the command for Docker container or Kubernetes
  2. pod, respectively: docker cp <src-path> <container>:<dest-path> …
    To copy a file from the container to the local file system, use: docker cp <container>:<src-path> <local-dest-path>

Does Docker COPY create directory?

From the dockerfile reference about COPY and ADD , it says Note: The directory itself is not copied, just its contents. , so you have to specify a dest directory explicitly.

How do I copy a file in Dockerfile?

To do so follow the below steps:

  • Step 1: Create a Directory to Copy. …
  • Step 2: Edit the Dockerfile. …
  • Step 3: Build the Docker Image. …
  • Step 4: Verifying the Docker Image. …
  • Step 5: Running the Docker Container. …
  • Step 6: Verify the Copying of the Directory.

How does copy work in Dockerfile?

COPY and ADD are both Dockerfile instructions that serve similar purposes. They let you copy files from a specific location into a Docker image. COPY takes in a src and destination. It only lets you copy in a local file or directory from your host (the machine building the Docker image) into the Docker image itself.

What are Docker layers?

Basically, a layer, or image layer is a change on an image, or an intermediate image. Every command you specify ( FROM , RUN , COPY , etc.) in your Dockerfile causes the previous image to change, thus creating a new layer.

How do I copy a docker image?

To export your image to a tar file, run the docker save command, specifying a name for the . tar file, and the docker image name. This will save the docker image locally.

Housekeeping on gitlab and practical examples using gitlab-ctl

In this section we will see some important housekeeping tasks while maintaining gitlab server.

We will list out some of the important configuration services present in gitlab and best housekeeping tips.
The important configuration file for gitlab is: /opt/gitlab/embedded/service/gitlab-rails/config/gitlab.yml
Once the changes are made to this file it should be followed up running the reconfigure to apply the changes.
The chef server reads the config files and then updates the system wide configuration resources.

Reconfiguring the gitlab

[vamshi@gitlab ~]$ sudo gitlab-ctl reconfigure

This command reloads the configuration from the configuration files and also migrated if any changes regiuired to the Postgresql database.

View all the current logs run the gitlab-ctl tail command.

[vamshi@node01 ~]$ sudo gitlab-ctl tail
==> /var/log/gitlab/gitlab-shell/gitlab-shell.log <==

==> /var/log/gitlab/gitlab-rails/sidekiq.log <==
2020-04-o2_13:30:24.29475 2020-04-02T13:30:24.293Z 8872 TID-or0k2ve5w PagesDomainVerificationCronWorker JID-e46ed1d452563ca9b7d4adca INFO: done: 0.357 sec
-- OUTPUT TRUNCATED --

This in one of the first command you need when troubleshooting your gitlab server..
This prints the logs from various components present in gitlab and you as an administrator will be able to effectively identify the issues.
To start the interactive ruby console and debug mostly used for Database interaction operations, it takes -e as argument and takes you to the production environment. -s takes you to the sandbox environment.

gitlab-rails console <-e|-s> [environment]

For example we can get the complete gitlab information using the following gitlab:env:info:

[vamshi@gitlab ~]$ sudo gitlab-rails gitlab:env:info
[sudo] password for vamshi:

System information
System: 
Proxy: no
Current User: git
Using RVM: no
Ruby Version: 2.5.3p105
Gem Version: 2.7.6
Bundler Version:1.17.3
Rake Version: 12.3.2
Redis Version: 3.2.12
Git Version: 2.18.1
GitLab information
Version: 11.10.4-ee
Revision: 88a3c791734

GitLab Shell
Version: 9.0.0

-- OUTPUT TRUNCATED --

Some more important commands for gitlab Houseeping:

[vamshi@gitlab ~]$ sudo gitlab-rails gitlab:check
[sudo] password for vamshi:
Checking GitLab subtasks ...

Checking GitLab Shell ...

-- OUTPUT TRUNCATED --

How to restart the gitlab serer from command line ?

[vamshi@gitlab ~]$ sudo gitlab-rails restart

How to clear the gitlab logs by truncating them to Zero bytes?

[vamshi@gitlab ~]$ sudo gitlab-rails log:clear

How To print the high level stats of gitlab server?

[vamshi@gitlab ~]$ sudo gitlab-rails stats

What is GitLab housekeeping?

GitLab supports and automates housekeeping tasks within your current repository such as: Compressing Git objects. Removing unreachable objects.

What is GitLab housekeeping?

How do I clean up GitLab repository?

  • To clean up a repository:
  • Go to the project for the repository.
  • Navigate to Settings > Repository.
  • Upload a list of objects. For example, a commit-map file created by git filter-repo which is located in the filter-
  • repo directory. …
  • Click Start cleanup.

What is Git repack?

DESCRIPTION. This command is used to combine all objects that do not currently reside in a “pack”, into a pack. It can also be used to re-organize existing packs into a single, more efficient pack.

What does Git prune do?

The git prune command is an internal housekeeping utility that cleans up unreachable or “orphaned” Git objects. Unreachable objects are those that are inaccessible by any refs. Any commit that cannot be accessed through a branch or tag is considered unreachable.

How do I know if GitLab is running?

When a user goes to your GitLab URL, they will be shown an arbitrary Deploy in progress page. To remove the page, you simply run sudo gitlab-ctl deploy-page down . You can also check the status of the deploy page with sudo gitlab-ctl deploy-page status.

How do I maintain a Git repository?

Manually reviewing large files in your repository

  • Download the script to your local system.
  • Put it in a well known location accessible to your Git repository.
  • Make the script an executable: …
  • Clone the repository to your local system.
  • Change directory to your repository root.
  • Run the Git garbage collector manually.

How do I purge Gitlab?

uninstall Gitlab:

  1. Stop the gitlab service. Command : sudo gitlab-ctl stop.
  2. Start commonde of service facility. command : sudo gitlab-ctl uninstall.
  3. Delete the package of gitlab. command : Locat gitlab.
  4. restart machine.

How do I empty a Gitlab project?

Delete a project

  1. On the top bar, select Menu > Projects and find your project.
  2. On the left sidebar, select Settings > General.
  3. Expand Advanced.
  4. In the “Delete project” section, select Delete project.
  5. Confirm the action when asked to.

Are git repos compressed?

Thirdly, Git stores its data as compressed objects, whereas SVN stores them as uncompressed copies. Go into any . svn/text-base directory, and you’ll find uncompressed copies of the (base) files.

SVN commands

SVN is Version controlling system and predates git, It was one of the most widely used version control system and served the community and still going on.. It had its own share advantages and shortcomings.

In this tutorial we will shed some light on practical usecases of SVN and day-to-day activities.

How to take a dump of live svn repo by loading it to another Repo on the fly.

# svnadmin dump /opt/svn/ProjectCode | svnadmin load /opt/svn/ProjectCode

SVN commands to take the dump from repo to a .dump file

# svnadmin dump /opt/svn/PST > test.dump

Using svn comands svnadmin to take the dump for specific revision number range from commandline.

# svnadmin dump -r 41:3601 /opt/svn/ProjectCode > test.dump

SVN Commands to split svn directories to respective svn repositories:

We have the folder structure of the ProjectCode and want to create a individual repository of all the folders with their own SVN repos, We can use the svndumpfilter to achieve the task.

$ cat projectslist
./project1./project2
./project3
./project4
$ for i in `cat projectslist`; do sudo svndumpfilter --drop-empty-revs --renumber-revs exclude `cat projectslist | grep -v $i` < SVN.dump > `echo $i | sed -e 's/\///g'`.dump; done

How to setup up a SVN repo from linux commandline.

Creating Dir for new SVN

# mkdir /opt/svn/ProjectCode

Initialize a repo in the newly created directory

#svnadmin create /opt/svn/ProjectCode

Load the repo from dump

#svnadmin load --force-uuid /opt/svn/ProjectCode < newProjectCode.dump

Loading repo from dump and redirecting output to file

#svnadmin load --force-uuid /opt/svn/ProjectCode < newProjectCode.dump >> /root/pst.out &

Linux Commands To delete a repo; Make sure the svnserve process is in stopper state and not active while removing the repo.

# rm -rf /opt/svn/PST

While taking SVN repo dump How to Exclude some paths from existing dump and create a new dump
We will be using the exclude option and passing the exclude pattern

# svndumpfilter exclude `cat ProjectCode-exclude-somerolders` < ProjectCode.dump > new-exclude.dump

Below is a sample exclude file with specific file names and directory paths

# cat ProjectCode-excludelist
/path/to/code/not/required
/Some/more/paths/and/specific-filenames.css
/code/static/test/

How to check the logs from SVN repo from commandline

# svn log file:///opt/svn/Project

How to setup SVN repository with configuration ?

# svnadmin create /opt/svn

Below is the example snippet from svnserve.conf

[general]
anon-access = none
auth-access = write
password-db = /opt/svn/conf/passwd
authz-db = /opt/svn/conf/authz

Here is the sample config snipet from authz

[/]
svamshi = rw

How to start SVN server from linux commandline

# svnserve --listen-host ip-address/project-repo -r /opt/svn/my-projectcode/ -d

How to checkout a SVN repo from linux commandline

# svn co --username=svamshi --password=mypassword svn://ip-address/project-repo

Adding the new created files to svn and then commit to svn.

# svn add linuxcent.html
# svn commit -am "updated with linuxcent.html"

How to serve the SVN repository through Apache Httpd server.

Example [/code]/opt/svn[/code]The svn module has to be downloaded

Below is the sample configuration of virtualhost informantion

subversion-apache-httpd-set-up-configuration

What are the svn commands?

Here are the basic SVN commands that every developer and admin should know.
svn admincreate. The svn admincreate command creates a new, empty repository.

  • svn import. …
  • svn checkout. …
  • svn commit. …
  • svn add. …
  • svn delete. …
  • svn list. …
  • svn diff.

How do I use svn in Linux?

  1. Connect via SSH. In order to install SVN, connect to your Linux VPS via SSH. …
  2. Update the OS Packages and Install SVN in Linux. If you are using an Ubuntu VPS, update the OS packages and install SVN on your server using the commands below: sudo apt-get update sudo apt-get install svn. …
  3. Check SVN Version

What is svn up command?

The svn update command lets you refresh your locally checked out repository with any changes in the repository HEAD on the server. It also tells you what has been changed, added, deleted. If a change has been made to a file you have also changed locally, svn will try to merge those changes.

How do I run svn?

  1. Open windows explorer.
  2. Create a folder where you will store project files.
  3. Right-click on the folder you created and select “SVN Checkout” (see image below).
  4. When prompted, enter your username and password.
  5. If everything worked, you now have a copy of the repository in your directory.

Which is Better Git or svn?

Why SVN Is Better Than Git

SVN is better than Git for architecture performance, binary files, and usability. And it may be better for access control and auditability, based on your needs.

Where are svn commands executed?

If you want to run Subversion commands from the command prompt, you should run the svn.exe command line client. TortoiseSVN 1.6.

How do I use shelve in svn?

To shelve your local changes, select your working copy and use Context Menu → Shelve The following dialog allows you to select the files you want to shelve and give a name under which you want to store them. If you select an existing shelf, then a new version is created for that shelf.

Does svn work on Linux?

SVN Installation

Subversion is a popular open-source version control tool. It is open-source and available for free over the internet. It comes by default with most of the GNU/Linux distributions, so it might be already installed on your system.

How configure svn server in Linux?

How to Install SVN Server on Ubuntu 18.04 & 16.04 LTS

  • Step 1 – Install Apache. …
  • Step 2 – Install SVN Server. …
  • Step 3 – Create First SVN Repository. …
  • Step 4 – Create Users for Subversion. …
  • Step 5 – Configure Apache with Subversion. …
  • Step 6 – Access Repository in Browser.

Where is svn installed on Linux?

Did you try whereis svn ? Executables are usually in /usr/bin or /usr/local/bin .

How do you svn add all files?

To add an existing file to a Subversion repository and put it under revision control, change to the directory with its working copy and run the following command: svn add file… Similarly, to add a directory and all files that are in it, type: svn add directory

How to start Jenkins on a different port

The jenkins Build and Integration application based on java programming language, tends to have its roots stuck to the typical Tomcat web server
Out of the box the jenkins starts up on the default port 8080 and this can be customized on the system or a new proxy routing can be setup which might add a slight overhead on the jenkins inbound requests,

How to change the Jenkins default Port?

We have the Jenkins default home located at /var/lib/jenkins all the configuration files are present in this location.
The important configuration although is /etc/sysconfig/jenkins which is present outside $JENKINS_HOME
The Jenkins Default JENKINS_PORT parameter is set to 8080

[root@node02 jenkins]# grep JENKINS_PORT /etc/sysconfig/jenkins
JENKINS_PORT="8080"

If you are on Debian or Ubuntu linux, then the relevant file will be /etc/default/jenkins
We will be now changing the variable $JENKINS_HOME to listen to the port 9090 and restarting the jenkins service.

[root@node02 jenkins]# systemctl restart jenkins.service

You can check for the port information from the ps -ef | grep jenkins output as follows or checkout from the netstat command

[root@node02 jenkins]# ps -ef |grep jenkins
jenkins 5110 1 90 23:04 ? 00:00:02 /etc/alternatives/java -Dcom.sun.akuma.Daemon=daemonized -Djava.awt.headless=true -DJENKINS_HOME=/var/lib/jenkins -jar /usr/lib/jenkins/jenkins.war --logfile=/var/log/jenkins/jenkins.log --webroot=/var/cache/jenkins/war --daemon --httpPort=9090 --debug=5 --handlerCountMax=100 --handlerCountMaxIdle=20

How do I change the default Jenkins port in Linux?

  1. First, run this command to open jenkins configurations: sudo nano /etc/default/jenkins.
  2. The only part you need to change is: #port for HTTP connector (default 8080; disable with -1) Http_port = 8080. …
  3. Finally, Restart Jenkins service by running this command: sudo service jenkins restart.

How do I change my local Jenkins port?

  1. Go to the directory where you installed Jenkins (by default, it’s under Program Files/Jenkins)
  2. Open the Jenkins.xml configuration file.
  3. Search –httpPort=8080 and replace the 8080 with the new port number that you wish.
  4. Restart Jenkins for changes to take effect.

How do I change my Jenkins port from 8080 to 80?

  1. Go to /etc/default folder –> Open the file “jenkins”
  2. Modify the line HTTP_PORT=8080 as HTTP_PORT=80.
  3. Start jenkins as root by using the command: sudo /etc/init.d/jenkins start.
  4. Open a browser and browse as localhost:80.

What port is Jenkins running on?

The default Jenkins installation runs on ports 8080 and 8443. Typically, HTTP/HTTPS servers run on ports 80 and 443, respectively. But these ports are considered privileged on Unix/Linux systems, and the process using them must be owned by root.

How do I start Jenkins on a different port?

How to change the default port in Jenkins

  1. Go to C:\Program Files (x86)\Jenkins (I’m using Windows Server 2012 and assuming it’s installed to default location)
  2. Open Jenkins.xml.
  3. Edit the –httpPort argument (you may need to edit default permissions)
  4. Restart the Jenkins service.
  5. Now Jenkins will permanently use the new port.

How do I run a Jenkins war on another port?

All you need to do:

  1. Goto Jenkins folder present in C:\Program Files (x86)
  2. Open a notepad or text pad and run them as administrator and then try opening the jenkins. xml file present in the jenkins folder.
  3. Change the port number as below: <arguments>-Xrs -Xmx256m -Dhudson. lifecycle=hudson. lifecycle.

How do I change my Jenkins URL?

Fixing a root url

  1. Go to Jenkins > Manage Jenkins > Configure System, and locate the section titled “Jenkins Location”. You should see the warning here as well.
  2. Replace “localhost” with a valid hostname.
  3. Click Save.

How do I start Jenkins manually in Linux?

Go to the Jenkins installation, open the cmd and run:

  1. To stop: jenkins.exe stop.
  2. To start: jenkins.exe start.
  3. To restart: jenkins.exe restart.

What is Jenkins port 50000?

Jenkins runs on Tomcat, which uses port 8080 as the default. -p 5000:5000 required to attach slave servers; port 50000 is used to communicate between master and slaves.

How do I run Jenkins on port 443?

Basic solution (complete):

  1. You need a “Java keystore” of the SSL-certificate you want to use. …
  2. Copy the certificate, private key and (if present) intermediate CAs to your Jenkins host. …
  3. Convert the certificate-files to one single-filed PKCS12 container. …
  4. Make sure, that the Java “keystore”-command is present.

docker CMD vs ENTRYPOINT

The ENTRYPOINT or CMD usually determine the single and main startup process inside the running container, The ENTRYPOINT and the CMD are the final Docker DSL invocation statements in a Dockerfile.A Dockerfile can not be complete without either one of them.

Both the ENTRYPOINT and CMD will execute a /bin/sh -c , but have significant differences.

ENTRYPOINT usually is straight forward with the and is often the statement that enables the  docker image as a runnable container. The ENTRYPOINT statement doesnot let the run time arguments get overwritten during the container runtime, instead the commands are passed on as arguments to the ENTRYPOINT, for Example when the container is started as docker run my-image -d, then the resultant -d argument is passed on as an argument to the ENTRYPOINT.
It means that only last ENTRYPOINT statement is valid in the Dockerfile

The ENTRYPOINT takes CMD as its arguments.

ENTRYPOINT command arg1 arg2

OR

ENTRYPOINT command
CMD ["arg1", "arg2"]
ENTRYPOINT ["java","-jar","app.jar"]
CMD ["-Dserver.port=8080"]

CMD on the other hand is subversive to the ENTRYPOINT.
CMD start statement can be overwritten with container arguments during the container runtime. The CMD does not execute anything at the build time.

CMD ["command","arg1", "arg2"]
CMD ["java","-Djava.security.egd=file:/dev/urandom","-jar","-Dserver.port=8080","app.jar"]

The major practical use with CMD is that the you will be able to overwrite the docker runtime command line arguments but you cannot override with you have ENTRYPOINT.

The CMD will be very beneficial in cases which require sending arguments to containers in runtime which in development and QA stages and is great for debugging environments.

The [] are not mandatory for ENTRYPOINT and CMD instruction statements inside Dockerfile but can be given for better readability when you have lot of arguments

What is the difference between CMD and run in Dockerfile?

RUN is an image build step, the state of the container after a RUN command will be committed to the container image. A Dockerfile can have many RUN steps that layer on top of one another to build the image. CMD is the command the container executes by default when you launch the built image.

What is the use of CMD in docker?

The CMD command​ specifies the instruction that is to be executed when a Docker container starts. This CMD command is not really necessary for the container to work, as the echo command can be called in a RUN statement as well. The main purpose of the CMD command is to launch the software required in a container.

What is docker ENTRYPOINT script?

entrypoint scripts are plugins that can be written in any language. inherited images can add to existing entrypoint scripts by simply adding to the /docker-entrypoint.

What is the purpose of ENTRYPOINT in Dockerfile?

In Dockerfiles, an ENTRYPOINT instruction is used to set executables that will always run when the container is initiated. Unlike CMD commands, ENTRYPOINT commands cannot be ignored or overridden—even when the container runs with command line arguments stated.

Can Dockerfile have multiple ENTRYPOINT?

According to the documentation however, there must be only one ENTRYPOINT in a Dockerfile.

What is Docker ENTRYPOINT Initdb?

3. 3. /docker-entrypoint-initdb. d/init. sql is executed the moment your database container starts running, while your entrypoint.sh is executed the moment your web container starts running.

Does docker start run ENTRYPOINT?

So yes, the ‘ CMD ‘ commands are executed after a ‘ docker start ‘.

Can Dockerfile have multiple CMD?

You are right, the second Dockerfile will overwrite the CMD command of the first one. Docker will always run a single command, not more. So at the end of your Dockerfile, you can specify one command to run.

What is in docker Run command?

The docker run command creates a container from a given image and starts the container using a given command. It is one of the first commands you should become familiar with when starting to work with Docker.

What is difference between CMD and entrypoint?

In a nutshell: CMD sets default command and/or parameters, which can be overwritten from command line when docker container runs. ENTRYPOINT command and parameters will not be overwritten from command line. Instead, all command line arguments will be added after ENTRYPOINT parameters.

What is the default entrypoint for docker?

/bin/sh -c
Docker defaults the entrypoint to /bin/sh -c . This means you’ll end up in a shell session when you start the container.

Bash How to Print Array

Bash How to Print Array

Arrays are collection of elements, The Arrays in bash are indexed from 0 (zero-based).
Below is the definition on an Array in Bash
my_array=(zero one two three four)

Now our array is defined.
Here is exactly how the my_array is stored on BASH:

my_array=([0]="zero" [1]="one" [2]="two" [3]="three" [4]="four")

You can explicit define an array:

declare -a MY_ARRAY

You can view the declarations along with other environment variables using the declare command.

declare -p my_array
declare -a my_array=([0]="zero" [1]="one" [2]="two" [3]="three" [4]="four")

Now if you try to print the array:

my_array=(zero one two three four)
echo $my_array
zero

By default only the first element value is printed which belongs to the 0 index.

To print the first element of the array using the indexing:

my_array=(zero one two three four)
echo ${my_array[0]}
zero

The change we noticed here is the use of the Curly Braces ‘{}’, its used to refer to the value of an item in the array. The curly braces are required to avoid issues with path name expansion.

To read all elements of the array use the symbols “@” or “*”.

echo ${my_array[@]}
zero one two three four
echo ${my_array[*]}
zero one two three four

The difference between “$@” and “$*” is “$@” expands each element as a separate argument, however “$*” expand to the arguments merged into one argument.

To prove this, print the index elements followed by $@ or $* format.

echo ${my_array[$*0]}
zero
echo ${my_array[$@1]}
one
echo ${my_array[$*2]}
two

Getting the Length of the Array

If you need to get the length of the array uses the symbol “#” before the name of the array:

echo "${#my_array[*]}"
5

How do I print an array in bash?

Print Bash Array

We can use the keyword ‘declare’ with a ‘-p’ option to print all the elements of a Bash Array with all the indexes and details. The syntax to print the Bash Array can be defined as: declare -p ARRAY_NAME.

How do I print in bash?

After typing in this program in your Bash file, you need to save it by pressing Ctrl +S and then close it. In this program, the echo command and the printf command is used to print the output on the console.

How do you print an array element in a new line in Shell?

To print each word on a new line, we need to use the keys “%s’\n”. ‘%s’ is to read the string till the end. At the same time, ‘\n’ moves the words to the next line. To display the content of the array, we will not use the “#” sign.

How do I display all array elements at once?

Program:
  1. public class PrintArray {
  2. public static void main(String[] args) {
  3. //Initialize array.
  4. int [] arr = new int [] {1, 2, 3, 4, 5};
  5. System. out. println(“Elements of given array: “);
  6. //Loop through the array by incrementing value of i.
  7. for (int i = 0; i < arr. length; i++) {
  8. System. out. print(arr[i] + ” “);

How do I create an array in bash?

  1. To declare your array, follow these steps:
    Give your array a name.
  2. Follow that variable name with an equal sign. The equal sign should not have any spaces around it.
  3. Enclose the array in parentheses (not brackets like in JavaScript)
  4. Type your strings using quotes, but with no commas between them.

How do you create an array in bash?

Define An Array in Bash

You have two ways to create a new array in bash script. The first one is to use declare command to define an Array. This command will define an associative array named test_array. In another way, you can simply create Array by assigning elements.

How does printf work in bash?

What Is the Bash printf Function? As the name suggests, printf is a function that prints formatted strings of text. That means you can write a string structure (the format) and later fill it in with values (the arguments). If you’re familiar with the C/C++ programming languages, you might already know how printf works.

How do you pass an array to a function in bash?

10 Answers

  1. Expanding an array without an index only gives the first element, use copyFiles “${array[@]}” instead of copyFiles $array.
  2. Use a she-bang #!/bin/bash.
  3. Use the correct function syntax. Valid variants are function copyFiles {… …
  4. Use the right syntax to get the array parameter arr=(“$@”) instead of arr=”$1″

How do you create an empty array in bash?

To declare an empty array, the simplest method is given here. It contains the keyword “declare” following a constant “-a” and the array name. The name of the array is assigned with empty parenthesis.

How do I get the size of an array in bash?

To get the length of an array, we can use the {#array[@]} syntax in bash. The # in the above syntax calculates the array size, without hash # it just returns all elements in the array.