[RndTbl] restarting a process via crontab?

[Peter O'Gorman]

On 06/13/2010 02:36 PM, athompso at athompso.net wrote:
>
> So far, the best solution I've come up with is a crontab entry (for me,
> not root):
>
> 0 * * * * if [ -f /home/athompso/.fetchmail.pid ];then read
> FP</home/athompso/.fetchmail.pid;if [ -d /proc/$FP -a -r /proc/$FP/exe
> ];then BIN=$(stat -c %N /proc/$FP/exe);BIN="${BIN#*->
> }";BIN="${BIN#\`}";BIN="${BIN%\'}";BIN=$(basename "${BIN}");if [ "$BIN" ==
> "fetchmail" ];then exit 0;fi;fi;fi;fetchmail

I would put the script into a file and run that from cron, it must be 
hard to maintain a crontab with more than a couple of entries like that :-)

>
> (or, more readably:)
>          if [ -f /home/athompso/.fetchmail.pid ]
>          then
>                  read FP<  /home/athompso/.fetchmail.pid
>                  if [ -d /proc/$FP -a -r /proc/$FP/exe ]
>                  then
>                          BIN=$(stat -c %N /proc/$FP/exe)

I'd use readlink(1) here.

>                          BIN="${BIN#*->  }"
>                          BIN="${BIN#\`}"
>                          BIN="${BIN%\'}"

Which should get rid of the above.

>                          BIN=$(basename "${BIN}")

Why do basename? BIN=${BIN##*/} saves a fork.

>                          if [ "$BIN" == "fetchmail" ]
>                          then
>                                  exit 0
>                          fi
>                  fi
>          fi
>          fetchmail

My script might look something like (typed in mail):

#!/bin/sh
pidfile=/home/athompso/.fetchmail.pid
BIN=
test -f $pidfile && read FP < $pidfile
test -d /proc/$FP && BIN=$(readlink /proc/$FP/exe)
case "${BIN}" in
   */fetchmail) ;;
   *) fetchmail ;;
esac

>
> FYI: I decided against using sed(1) to parse the output because doing it
> this way saves two fork(2)s and one exec(2).  I know I don't need to worry
> about efficiency on a dual-Xeon server, but I'm trying to stay in the habit
> because I'm also working on 200MHz ARM5 platforms where it does matter.
>

Yes, forking is expensive.

Peter