RBASH

   1 6.10 The Restricted Shell
   2 =========================
   3
   4 If Bash is started with the name 'rbash', or the '--restricted' or '-r'
   5 option is supplied at invocation, the shell becomes restricted.  A
   6 restricted shell is used to set up an environment more controlled than
   7 the standard shell.  A restricted shell behaves identically to 'bash'
   8 with the exception that the following are disallowed or not performed:
   9
  10    * Changing directories with the 'cd' builtin.
  11    * Setting or unsetting the values of the 'SHELL', 'PATH', 'ENV', or
  12      'BASH_ENV' variables.
  13    * Specifying command names containing slashes.
  14    * Specifying a filename containing a slash as an argument to the '.'
  15      builtin command.
  16    * Specifying a filename containing a slash as an argument to the '-p'
  17      option to the 'hash' builtin command.
  18    * Importing function definitions from the shell environment at
  19      startup.
  20    * Parsing the value of 'SHELLOPTS' from the shell environment at
  21      startup.
  22    * Redirecting output using the '>', '>|', '<>', '>&', '&>', and '>>'
  23      redirection operators.
  24    * Using the 'exec' builtin to replace the shell with another command.
  25    * Adding or deleting builtin commands with the '-f' and '-d' options
  26      to the 'enable' builtin.
  27    * Using the 'enable' builtin command to enable disabled shell
  28      builtins.
  29    * Specifying the '-p' option to the 'command' builtin.
  30    * Turning off restricted mode with 'set +r' or 'set +o restricted'.
  31
  32 These restrictions are enforced after any startup files are read.
  33
  34 When a command that is found to be a shell script is executed (*note
  35 Shell Scripts::), 'rbash' turns off any restrictions in the shell
  36 spawned to execute the script.
  37