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Diffstat (limited to 'RBASH')
| -rw-r--r-- | RBASH | 51 |
1 files changed, 51 insertions, 0 deletions
@@ -0,0 +1,51 @@ +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', 'HISTFILE', + '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 + 'history' 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 (*note +Shell Scripts::), 'rbash' turns off any restrictions in the shell +spawned to execute the script. + +The restricted shell mode is only one component of a useful restricted +environment. It should be accompanied by setting 'PATH' to a value that +allows execution of only a few verified commands (commands that allow +shell escapes are particularly vulnerable), leaving the user in a +non-writable directory other than his home directory after login, not +allowing the restricted shell to execute shell scripts, and cleaning the +environment of variables that cause some commands to modify their +behavior (e.g., 'VISUAL' or 'PAGER'). + +Modern systems provide more secure ways to implement a restricted +environment, such as 'jails', 'zones', or 'containers'. + |