RESTRICTED SHELL
       If bash is started with the name rbash, or the  -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.  It behaves identi-
       cally to bash with the exception that  the  following  are
       disallowed or not performed:
 
       o      changing directories with cd
 
       o      setting  or  unsetting  the  values of SHELL, PATH,
              ENV, or BASH_ENV
 
       o      specifying command names containing /
 
       o      specifying a file name containing a / as  an  argu-
              ment to the .  builtin command
 
       o      Specifying  a  filename  containing  a  slash as an
              argument to the -p option to the hash builtin  com-
              mand
 
       o      importing function definitions from the shell envi-
              ronment at startup
 
       o      parsing the value of SHELLOPTS from the shell envi-
              ronment at startup
 
       o      redirecting output using the >, >|, <>, >&, &>, and
              >> redirection operators
 
       o      using the exec builtin command to replace the shell
              with another command
 
       o      adding or deleting builtin commands with the -f and
              -d options to the enable builtin command
 
       o      specifying the -p option  to  the  command  builtin
              command
 
       o      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 exe-
       cuted (see COMMAND EXECUTION above), rbash turns  off  any
       restrictions in the shell spawned to execute the script.