RSH(8) Maintenance Procedures RSH(8)


rsh, restricted_shell - restricted shell command interpreter


/usr/lib/rsh [-acefhiknprstuvx] [argument]...


rsh is a limiting version of the standard command interpreter sh, used to
restrict logins to execution environments whose capabilities are more
controlled than those of sh (see sh(1) for complete description and

When the shell is invoked, it scans the environment for the value of the
environmental variable, SHELL. If it is found and rsh is the file name
part of its value, the shell becomes a restricted shell.

The actions of rsh are identical to those of sh, except that the
following are disallowed:

o changing directory (see cd(1)),

o setting the value of $PATH,

o specifying path or command names containing /,

o redirecting output (> and >>).

The restrictions above are enforced after .profile is interpreted.

A restricted shell can be invoked in one of the following ways:

1. rsh is the file name part of the last entry in the /etc/passwd
file (see passwd(5));

2. the environment variable SHELL exists and rsh is the file name
part of its value; the environment variable SHELL needs to be
set in the .login file;

3. the shell is invoked and rsh is the file name part of argument

4. the shell is invoked with the -r option.

When a command to be executed is found to be a shell procedure, rsh
invokes sh to execute it. Thus, it is possible to provide to the end-user
shell procedures that have access to the full power of the standard
shell, while imposing a limited menu of commands; this scheme assumes
that the end-user does not have write and execute permissions in the same

The net effect of these rules is that the writer of the .profile (see
profile(5)) has complete control over user actions by performing
guaranteed setup actions and leaving the user in an appropriate directory
(probably not the login directory).

The system administrator often sets up a directory of commands (that is,
/usr/rbin) that can be safely invoked by a restricted shell. Some systems
also provide a restricted editor, red.


Errors detected by the shell, such as syntax errors, cause the shell to
return a non-zero exit status. If the shell is being used non-
interactively execution of the shell file is abandoned. Otherwise, the
shell returns the exit status of the last command executed.


Intro(1), cd(1), login(1), rsh(1), sh(1), exec(2), passwd(5), profile(5),


The restricted shell, /usr/lib/rsh, should not be confused with the
remote shell, /usr/bin/rsh, which is documented in rsh(1).

November 1, 1993 RSH(8)