Customizing the z/OS UNIX shells

After a user logs in to the shell, the system initializes the shell for that user. During the initialization, the system does the following:

Determines whether the user is authorized to use the shell by checking for a UID value in the user's RACF® user profile. It also checks that the user's RACF group has a GID assigned to it.
Sets the LOGNAME, HOME, and SHELL environment variables from data in the RACF user profile, which was specified in the RACF ADDUSER and ALTUSER commands. See Customizing the RACF user profile.
Connects the user to the initial working directory that was identified in the HOME environment variable in the RACF user profile. If the RACF user profile does not identify a working directory, the system uses the root as the user's working directory and issues a message.
Invokes the shell named in the PROGRAM statement of the OMVS segment in the RACF user profile.
- For the z/OS shell, it is named /bin/sh.
- For the tcsh shell, it is named /bin/tcsh.

Similar systems typically have an /etc/passwd file, which contains the HOME and PROGRAM environment variables. The file also contains the passwords and password phrases that are used. To provide better security, the z/OS shell does not use the /etc/passwd file; instead, it uses the initial values assigned to these variables in the RACF user profiles. RACF maintains the passwords and password phrases.