Chsh

chsh (an abbreviation of "change shell") is a command on Unix-like operating systems that is used to change a login shell.  Users can either supply the pathname of the shell that they wish to change to on the command line, or supply no arguments, in which case  allows the user to change the shell interactively.

Usage
 is a setuid program that modifies the  file, and only allows ordinary users to modify their own login shells.  The superuser can modify the shells of other users, by supplying the name of the user whose shell is to be modified as a command-line argument.  For security reasons, the shells that both ordinary users and the superuser can specify are limited by the contents of the  file, with the pathname of the shell being required to be exactly as it appears in that file.  (This security feature is alterable by re-compiling the source code for the command with a different configuration option, and thus is not necessarily enabled on all systems.) The superuser can, however, also modify the password file directly, setting any user's shell to any executable file on the system without reference to  and without using .

On most systems, when  is invoked without the  command-line option (to specify the name of the shell), it prompts the user to select one.  On Mac OS X, if invoked without the  option,  displays a text file in the default editor (initially set to vim) allowing the user to change all of the features of their user account that they are permitted to change, the pathname of the shell being the name next to "Shell:".  When the user quits vim, the changes made there are transferred to the /etc/passwd file which only root can change directly.   

Using the  option (for example: ) greatly simplifies the task of changing shells.

Depending on the system,  may or may not prompt the user for a password before changing the shell, or entering interactive mode.  On some systems, use of  by non-root users is disabled entirely by the sysadmin.

On many Linux distributions, the  command is a PAM-aware application.  As such, its behaviour can be tailored, using PAM configuration options, for individual users.  For example, an  directive that specifies the  module can be used to deny  access to individual users, by specifying a file of the usernames to deny access to with the  option to that module (along with the  option).

Portability
POSIX does not describe utilities such as , which are used for modifying the user's entry in .  Most Unix-like systems provide .  SVr4-based systems provided a similar capability with passwd.  Two of the three remaining systems (IBM AIX and HP-UX) provide  in addition to .  The exception is Solaris, where non-administrators are unable to change their shell unless a network name server such as NIS or NIS+ is installed.  The obsolete SGI SVr4 system IRIX64 also lacked .

See also
 Comparison of command shells

References

Further reading
  — some examples of invoking  with the  and  options

External links

 
 
 
 

Category:Unix user management and support-related utilities
Category:Standard Unix programs