rbash: restricted bash
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 identically to bash with the exception that the following are disallowed or not performed:
changing directories with cd
setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV
specifying command names containing /
specifying a file name containing a / 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 command to replace the shell with another command
adding or deleting builtin commands with the -f and -d options to the enable builtin command
Using the enable builtin command to enable disabled shell builtins
specifying the -p option to the command builtin command
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, rbash turns off any restrictions in the shell spawned to execute the script
