I would like cron to only email on stderr output but when it does it should include all stdout and stderr
This is different than the usual question of only emailing on stderr (ie. redirect stdout to /dev/null). In that case, cron only emails the stderr but I would like to see everything for context.
I'm running Rocky 9 with cronie as the cron daemon.
If the command exits with a non-zero status code, you could try:
bash -c 'command 2>&1 > /tmp/err || mail -A /tmp/err [email protected]' where:
bash -c '' enables using multiple commands on a cronjob; you could use a script, too.command is path to the command to be excuted2>&1 redirects stderr to stdout> /tmp/err saves stdout (now both streams) to a file (path /tmp/err)|| runs the second command only if the first failed with a non-zero status codemail -A /tmp/err sends the file as an attachment mail [email protected] < /tmp/err would send it as the message bodyYou could enhance this using, e.g. mktemp to use different path for every log in case of simultaneous runs & sleep there is something missing from the end of the file.
I decided to write a script that could approximate a solution to the question of only emailing on stderr output.
The key is storing stdout/stderr to files until stderr is detected and then outputting the combined file.
The combined file can loosely be said to retain stdout/stderr order in so far as tail can iterate over its files quickly enough. If there's no buffering and a command takes more than a second or two and there's some delay between stdout/stderr ouputs then this approach can approximate ordered stdout/stderr output.
I call this script cron-wrapper.sh. It's purpose is to accept a command and arguments and run them.
It's intended to be called from a crontab like this:
30 * * * * root sh cron-wrapper.sh sh cron-job.sh >/dev/null
Note that when outputing everything on stderr "everything" is output to stderr not stdout to fulfill my requirement that cron email everything on stderr output
Script:
#!/bin/bash # Input cmd=$1 shift # Run given command in background so we can tail output files immediately stdoutFile=`mktemp` stderrFile=`mktemp` $cmd "${@}" >"$stdoutFile" 2>"$stderrFile" & cmdPid=$! # Tail stdout and stderr files teeFile=`mktemp` tail -F -s 0.01 --pid=$cmdPid --quiet --silent "$stdoutFile" "$stderrFile" | tee "$teeFile" # Output everything if stderr output detected if [ -s "$stderrFile" ]; then cat "$teeFile" >&2 fi # Clean up rm -f "$stdoutFile" "$stderrFile" "$teeFile" Use cronic which does exactly that. From the web page:
Cronic is a small shim shell script for wrapping cron jobs so that cron only sends email when an error has occurred. Cronic defines an error as any non-trace error output or a non-zero result code.
Example:
# Do the thing as 23:42 every day. 42 23 * * * cronic /root/.local/bin/doit.sh 
teein.