Restricted Shells (UNIX in a Nutshell: System V Edition)

4.8. Restricted Shells

Restricted shells can be invoked in any of the following ways:

rksh		Korn shell
ksh -r
set -r

/usr/lib/rsh	Bourne shell
set -r

Restricted shells can also be set up by supplying the full pathname to rksh or rsh in the shell field of /etc/passwd or by using them as the value for the SHELL variable.

Restricted shells act the same as their nonrestricted counterparts, except that the following are prohibited:

Changing directory (i.e., using cd).
Setting the PATH variable. rksh also prohibits setting ENV and SHELL.
Specifying a / for command names or pathnames.
Redirecting output (i.e., using > and >>). ksh also prohibits the use of <>.
Adding new built-in commands (ksh93).

Shell scripts can still be run, since in that case the restricted shell calls ksh or sh to run the script. This includes the /etc/profile, $HOME/.profile, and $ENV files.

Restricted shells are not used much in practice, as they are difficult to set up correctly.