UNIX -LINUX – Difference between Login Shell and Non-Login Shell

Login Shell and Non-Login Shell:

Login shells:

• A Login shell is started after a successful login, using /bin/login, by reading the /etc/passwd file. Login shell is the first process that executes under our user ID when we log in to a session.
• The login process tells the shell to behave as a login shell with a convention: passing argument 0, which is normally the name of the shell executable, with a “-” character prepended.
• For example, for Bash shell it will be -bash.
• When Bash is invoked as a Login shell;

→Login process calls /etc/profile
→/etc/profile calls the scripts in /etc/profile.d/
→Login process calls ~/.bash_profile
→~/.bash_profile calls ~/.bashrc
→~/.bashrc calls /etc/bashrc

• Login shells include the following.
• Shells created by explicitly telling to login.

examples:

# su - | # su -l | # su --login | # su USERNAME - | # su -l USERNAME | # su --login       USERNAME | # sudo -i

• Shells created at login, including X login.
• A Login shell can be recognized by the following procedure.
• Execute the below command in shell.

        # echo $0

• If the output is the name of our shell, prepended by a dash, then it is a login shell.
• For example -bash, -su etc.

Non login shells:

• A Non login shell is started by a program without a login. In this case, the program just passes the name of the shell executable.
• For example, for a Bash shell it will be simply bash.
• When bash is invoked as a Non login shell;

→Non-login process(shell) calls ~/.bashrc
→~/.bashrc calls /etc/bashrc
→/etc/bashrc calls the scripts in /etc/profile.d/

• Non login shells include the following.
• Shells created using the below command syntax.

examples:

# su | # su USERNAME

• Graphical terminals
• Executed scripts
• Any other bash instances

• A Non login shell can be recognized by the following procedure.
• Execute the below command in shell.

# echo $0

• If the output is the name of our shell, does not prepend by a dash, then it is a Non login shell.
• For example bash, su etc.