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author | W. Trevor King <wking@tremily.us> | 2013-03-06 12:02:59 -0500 |
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committer | Matt Turner <mattst88@gmail.com> | 2013-10-26 10:23:23 -0700 |
commit | 5c96523ac65eb09f5144d54bcaf374e75e244762 (patch) | |
tree | 0b9f89d38b9cd8f9476d98fc32cf233c51666393 | |
parent | livecd-bashrc: Avoid a startx race by restricting to tty1 (diff) | |
download | catalyst-5c96523ac65eb09f5144d54bcaf374e75e244762.tar.gz catalyst-5c96523ac65eb09f5144d54bcaf374e75e244762.tar.bz2 catalyst-5c96523ac65eb09f5144d54bcaf374e75e244762.zip |
livecdfs-update.sh: Use `bash --login` to spawn startx
Starting a "login" version of Bash via `su` is tricky. The naive:
su - ${first_user} -c startx
fails because `su - ...` clears a number of environment variables (so
the prefixed `source /etc/profile` doesn't accomplish anything), but
Bash isn't started with the `--login` option, so it doesn't source
/etc/profile internally. From bash(1):
A login shell is one whose first character of argument zero is a -,
or one started with the --login option.
...
An interactive shell is one started without non-option arguments and
without the -c option whose standard input and error are both
connected to terminals (as determined by isatty(3)), or one started
with the -i option...
...
When bash is invoked as an interactive login shell, or as a
non-interactive shell with the --login option, it first reads and
executes commands from the file /etc/profile, if that file exists.
After reading that file, it looks for ~/.bash_profile,
~/.bash_login, and ~/.profile, in that order, and reads and executes
commands from the first one that exists and is readable. The
--noprofile option may be used when the shell is started to inhibit
this behavior.
In order to get the login-style profile loading with a non-interactive
`su` invocation, you need to use something like:
echo "${command}" | su - "${user}"
This starts a login shell and pipes the command in via stdin, which
seems to fake Bash into thinking its running from an interactive
terminal. Not the most elegant, but the other implementations I can
think of are even worse:
su - "${user}" -c "bash --login -c ${command}"
su - "${user}" -c 'source /etc/profile &&
(source .bash_profile || ...) && ${command}"
The old expression was broken anyway due to unescaped ampersands in
the sed expression. From sed(1):
s/regexp/replacement/
Attempt to match regexp against the pattern space. If successful,
replace that portion matched with replacement. The replacement
may contain the special character & to refer to that portion of
the pattern space which matched, and the special escapes \1
through \9 to refer to the corresponding matching sub-expressions
in the regexp.
This means that the old expression (with unescaped ampersands) lead
to:
source /etc/profile ##STARTX##STARTX su - ${first_user} -c startx
with ${first_user} expanded. This commented out startx, so it was
never run.
Reviewed-by: Matt Turner <mattst88@gmail.com>
-rw-r--r-- | targets/support/livecdfs-update.sh | 4 |
1 files changed, 1 insertions, 3 deletions
diff --git a/targets/support/livecdfs-update.sh b/targets/support/livecdfs-update.sh index f8eb4257..2b41f9d0 100644 --- a/targets/support/livecdfs-update.sh +++ b/targets/support/livecdfs-update.sh @@ -377,9 +377,7 @@ esac # We want the first user to be used when auto-starting X if [ -e /etc/startx ] then - sed -i \ - "s:##STARTX:source /etc/profile && su - ${first_user} -c startx:" \ - /root/.bashrc + sed -i "s:##STARTX:echo startx | su - '${first_user}':" /root/.bashrc fi if [ -e /lib/rcscripts/addons/udev-start.sh ] |