Friday, 15 April 2011

git import

I had a set of old files with the correct timestamp on, relating to separate versions of a file, ie, foo_16.c, foo_17.c, ... foo_22.c which I wanted to import into a new git repo while preserving the author history

so, this little snippet of code worked - may be useful for others

 
$ git init
$ git add -N foo.c
$ for i in `seq 16 22` ; do
cp -p hist/foo_$i.c foo.c;
GIT_COMMITTER_DATE="`date -R -r foo.c`" git commit \
--author "Fred Bloggs <fred.bloggs@example.com>" \
--date="`date -R -r foo.c`" -m "Version $i" foo.c
done


which you can then branch and commit as normal with current changes

Yes I could probably have done GIT_AUTHOR_DATE=$GIT_COMMITTER_DATE but well, 2 calls to date wasn't that much of an overhead in this case.

anyway, for those that care, the result is up on github

Monday, 4 April 2011

Bash, PS1, PROMPT_COMMAND and other fun

I've just spent 30 mins trying to understand the flow between the various files that set a bash prompt on fedora to do the following: (assumption is here that you're in a colour xterm)

I want:
* my username to change colour depending if I still have a valid kerberos token
* the hostname of the machine I'm on to be in RED if I'm root
* displayed path to be as simple as possible
* $ if I'm a minion, # if root as mormal
* command line editing to work sensibly, no wierdisms on wrapping long lines

so - I used to have on my machine something like the following:
if [ "$PS1" != "" ] ; then
klist -s
if [ $? -eq 0 ] ; then
PS1='\[\033[32m\]\u@\h\[\033[0m\]:\w\$ '
else
PS1='\[\033[36m\]\u\[\033[32m\]@\h\[\033[0m\]:\w\$ '
fi
fi

and something similar for root.

But on my laptop (F14) I wanted it system wide, so went down the approach of customising /etc/bashrc where you find calls to
PROMPT_COMMAND=/etc/sysconfig/bash-prompt-xterm

1) /etc/sysconfig/bash-prompt-* aren't included, so you're on your own
2) It must point to an executable script that is run every time before displaying the prompt
3) PS1 is still displayed *AND* if you use tab completion / ctrl-l, its *only* PS1 thats displayed on your screen, not the output from PROMPT_COMMAND

so: DON'T do the following:

cat /etc/sysconfig/bash-prompt-xterm
#!/usr/bin/env bash
# set green username if we have a valid kerberos token, else cyan
klist -s
if [ $? -eq 0 ] ; then
K='[32m'
else
K='[36m'
fi
# set hostname in red if we're root, green otherwise
if [ ${USER} = 'root' ] ; then
U='[31m'
else
U='[32m'
fi

printf "^[%s%s^[[37m@^[%s%s^[[0m:%s " ${K} ${USER} ${U} ${HOSTNAME%%.*} "${PWD/#$HOME/~}"
#echo -ne "\033]0;${USER}@${HOSTNAME%%.*}:${PWD/#$HOME/~}\007"
(where ^[ is 'ctrl-v, esc' in vim)
because you end up with stuff like

aelwell@pcitgtelwell:~[aelwell@pcitgtelwell ~]$

until you press ctrl-l and end up with just
[aelwell@pcitgtelwell ~]$ (ie, $PS1)


but *DO* make the call to see if you have a valid token and set the xterm titlebar in /etc/sysconfig/bash-prompt-xterm, but if you're altering PS1, then do so in the traditional places of /etc/bashrc and (as suggested in that file) a custom modification shell script in /etc/profile.d/ directory.

Ho Hum. Hope this clears up for anyone else trying to work out what the sysconfig/bash-prompt-* files do.

oh, and does anyone know a lighter call to see if a token is still valid than 'klist -s'?

Friday, 1 April 2011

Daily WTF Candiate

(Credit for spotting this one goes over to the fine folks at scotgrid who were bitten by the fallout.

Anyway, Useless Use of Cat^H^H^HMore award goes to http://bit.ly/dI2W3c

Plotting Lustre MDS stats

At $dayjob we have several large filesystems - for example our /scratch system has 3.1 PB of space using over 1000 HDDs. Although each vendo...