RSH(1M)RSH(1M)NAME
rsh, restricted_shell - restricted shell command interpreter
SYNOPSIS
/usr/lib/rsh [-acefhiknprstuvx] [argument]...
DESCRIPTION
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 usage).
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 fol‐
lowing are disallowed:
o changing directory (see cd(1)),
o setting the value of $PATH,
o pecifying 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(4));
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 argu‐
ment 0;
4. the shell is invoke 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 stan‐
dard 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 directory.
The net effect of these rules is that the writer of the .profile (see
profile(4)) has complete control over user actions by performing guar‐
anteed 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.
EXIT STATUS
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-interac‐
tively execution of the shell file is abandoned. Otherwise, the shell
returns the exit status of the last command executed.
SEE ALSOintro(1), cd(1), login(1), rsh(1), sh(1), exec(2), passwd(4), pro‐
file(4), attributes(5)NOTES
The restricted shell, /usr/lib/rsh, should not be confused with the
remote shell, /usr/bin/rsh, which is documented in rsh(1).
Nov 1, 1993 RSH(1M)
