Differences between Login and Non-Login Shells
This article explains the difference between login shells and non-login shells in UNIX-based systems.
What is Shell in UNIX based systems
The shell in UNIX based systems is the interface between the user and the kernel of the operating system. It takes input from the user and sends it to the kernel and takes the result from the kernel to the user.
There are two types of shells, login shells and non-login shells.
Each shell executes a series of startup scripts after startup to set up the environment. These scripts have different purposes, and they all affect the environment.
Subsequent scripts can overwrite values set by earlier scripts.
What is a Login Shell in UNIX based systems
A login shell is the first process started after a successful login /bin/loginby reading /etc/passwdthe .login file. A login shell executes under your user ID.
A login shell is executed when you log in using a terminal, switch to another user, or use SSH.
Once a login shell starts, it executes a set of startup scripts to set up the shell environment. The following scripts are executed.
The following command is used to indicate whether the shell is a login shell.
echo $0
Getting -bashor -suas output indicates that the shell is a login shell. Note -the symbol before the output.
In the following figure, echo $0the output of the command bashhas a in front of -. It indicates that the shell is a login shell.
What is a non-login shell in UNIX based systems
A login shell starts a non-login shell. This can be a shell started as a process that is not logged in, or a shell started from another shell. The process starts a non-login shell using the name of the shell executable file.
Running a bash shell as a non-login shell executes the following script.
To determine if your shell is a non-login shell, run the following command.
echo $0
If the output is bashor suwithout a preceding -_, the shell is a non-login shell.
We execute the command in the figure below echo $0, and the output shows bashthe previous one -. This means we are using a login shell.
To start a non-login shell, we enter the name of the shell executable, in our case bash. We execute echo $0the command again to see what type of shell the newly started shell is; echothe output of the command is bash. -This means that the new shell is a non-login shell.
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