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Bash Reference Manual

6.10 The Restricted Shell

If Bash is started with the name rbash, or the `--restricted' or `-r' option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. A restricted shell behaves identically to bash with the exception that the following are disallowed or not performed:

• Changing directories with the cd builtin.
• Setting or unsetting the values of the SHELL, PATH, ENV, or BASH_ENV variables.
• Specifying command names containing slashes.
• Specifying a filename containing a slash as an argument to the . builtin command.
• Specifying a filename containing a slash as an argument to the `-p' option to the hash builtin command.
• Importing function definitions from the shell environment at startup.
• Parsing the value of SHELLOPTS from the shell environment at startup.
• Redirecting output using the `>', `>|', `<>', `>&', `&>', and `>>' redirection operators.
• Using the exec builtin to replace the shell with another command.
• Adding or deleting builtin commands with the `-f' and `-d' options to the enable builtin.
• Using the enable builtin command to enable disabled shell builtins.
• Specifying the `-p' option to the command builtin.
• Turning off restricted mode with `set +r' or `set +o restricted'.

These restrictions are enforced after any startup files are read.

When a command that is found to be a shell script is executed (see section 3.8 Shell Scripts), rbash turns off any restrictions in the shell spawned to execute the script.