Difference between revisions of "Dash as /bin/sh"

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==Relinking /bin/sh==
 
==Relinking /bin/sh==
Once you have verified that it won't break any functionality, it should be safe to relink {{ic|/bin/sh}}. To do so use the following command (as root):
+
Once you have verified that it won't break any functionality, it should be safe to relink {{ic|/bin/sh}}. To do so use the following command:
 
+
# ln -sfT /bin/dash /bin/sh
  ln -sfT /bin/dash /bin/sh
+
Updates of Bash could overwrite {{ic|/bin/sh}}. To prevent this, add the following line to the [option] section of {{ic|/etc/pacman.conf}}:
 +
NoExtract  = bin/sh

Revision as of 21:18, 10 April 2013

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Reason: please use the first argument of the template to provide a brief explanation. (Discuss in Talk:Dash as /bin/sh#)

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Reason: please use the first argument of the template to provide a brief explanation. (Discuss in Talk:Dash as /bin/sh#)

Dash is a minimalist POSIX-compliant shell. It can be much faster than Bash, and takes up less memory when in use. Most POSIX compliant scripts specify /bin/sh at the first line of the script, which means it will run /bin/sh as the shell, which by default in Arch is a symlink to /bin/bash.

You can re-symlink /bin/sh to /bin/dash, which can increase system performance, but first you must verify that none of the scripts that aren't explicitly #!/bin/bash scripts are safely POSIX compliant and do not require any of Bash's features.

This article is for those who want to help dash become the new /bin/sh.

From http://article.gmane.org/gmane.linux.arch.devel/11418:

Identifying bashisms

Features of bash that aren't included in Dash ('bashisms') will not work without being explicitly pointed to /bin/bash. The following instructions will allow you to find any scripts that may need modification.

Install checkbashismsAUR from the AUR.

Common places to check

  • Installed scripts with a #!/bin/sh shebang:
$ find {,/usr}/bin -type f \
    -exec grep -q -- '^#!/bin/sh' {} \; \
    -exec checkbashisms -f -p {} +
  • Package install scripts:
$ find /var/lib/pacman/local -mindepth 2 -type f -name install \
    -exec checkbashisms -f -p {} + 2>&1 |\
    grep -v -e '^you may get strange results' \
            -e 'does not appear to have a #! interpreter line;$'
  • Initscripts and daemons:
$ find \
    /etc/rc.{conf,d,local{,.shutdown},multi,shutdown,single,sysinit} -type f \
    -exec checkbashisms -f -p {} + 2>&1 |\
    grep -v -e '^you may get strange results' \
            -e 'does not appear to have a #! interpreter line;$'

Relinking /bin/sh

Once you have verified that it won't break any functionality, it should be safe to relink /bin/sh. To do so use the following command:

# ln -sfT /bin/dash /bin/sh

Updates of Bash could overwrite /bin/sh. To prevent this, add the following line to the [option] section of /etc/pacman.conf:

NoExtract   = bin/sh