---
name: "smrsh"
section: "8"
platform: "linux"
package: "sendmail-bin"
version: "8.18.1-6+b1"
release: "Debian 13 (Trixie)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/smrsh"
---

# smrsh(8)

restricted shell for sendmail

## NAME

smrsh - restricted shell for sendmail

## SYNOPSIS

**smrsh** **-c** command

## DESCRIPTION

The *smrsh* program is intended as a replacement for *sh* for use in the \`\`prog'' mailer in [*sendmail*(8)](/sendmail/8.md) configuration files. It sharply limits the commands that can be run using the \`\`\|program'' syntax of *sendmail* in order to improve the over all security of your system. Briefly, even if a \`\`bad guy'' can get sendmail to run a program without going through an alias or forward file, *smrsh* limits the set of programs that he or she can execute.

Briefly, *smrsh* limits programs to be in a single directory, by default /etc/mail/smrsh, allowing the system administrator to choose the set of acceptable commands, and to the shell builtin commands \`\`exec'', \`\`exit'', and \`\`echo''. It also rejects any commands with the characters \`\`', \`\<', \`\>', \`;', \`$', \`(', \`)', \`\\r' (carriage return), or \`\\n' (newline) on the command line to prevent \`\`end run'' attacks. It allows \`\`\|\|'' and \`\`&&'' to enable commands like: \`\`"\|exec /usr/local/bin/filter \|\| exit 75"''

Initial pathnames on programs are stripped, so forwarding to \`\`/usr/ucb/vacation'', \`\`/usr/bin/vacation'', \`\`/home/server/mydir/bin/vacation'', and \`\`vacation'' all actually forward to \`\`/etc/mail/smrsh/vacation''.

System administrators should be conservative about populating the sm.bin directory. For example, a reasonable additions is [*vacation*(1)](/vacation/1.md), and the like. No matter how brow-beaten you may be, never include any shell or shell-like program (such as [*perl*(1)](/perl/1.md)) in the sm.bin directory. Note that this does not restrict the use of shell or perl scripts in the sm.bin directory (using the \`\`#!'' syntax); it simply disallows execution of arbitrary programs. Also, including mail filtering programs such as [*procmail*(1)](/procmail/1.md) is a very bad idea. [*procmail*(1)](/procmail/1.md) allows users to run arbitrary programs in their [*procmailrc*(5)](/procmailrc/5.md).

## COMPILATION

Compilation should be trivial on most systems. You may need to use -DSMRSH\_PATH=\\"*path*\\" to adjust the default search path (defaults to \`\`/bin:/usr/bin:/usr/ucb'') and/or -DSMRSH\_CMDDIR=\\"*dir*\\" to change the default program directory (defaults to \`\`/etc/mail/smrsh'').

## FILES

/etc/mail/smrsh - default directory for restricted programs on most OSs

/var/adm/sm.bin - directory for restricted programs on HP UX and Solaris

/usr/libexec/sm.bin - directory for restricted programs on FreeBSD (\>= 3.3) and DragonFly BSD

## SEE ALSO

[sendmail(8)](/sendmail/8.md)