Linux: Detecting potential disk space problems before going home

As is typical in sysadmin work, one member of my team is always on call, having to be available during the night and on weekends. Sometimes the problems are big (especially hardware failures), sometimes they’re trivial, and sometimes they’re false alarms, but one thing is always true: it’s not fun to be woken up by a ringing phone, especially when you’re already not having enough sleep.

One of the most common reasons for being called at night (or during weekends) is when a disk’s occupation exceeds a threshold (let’s say 95%, although that value varies in reality). Logs get larger (especially when some error is constantly occurring), old logs aren’t compressed/rotated/deleted automatically, users leave huge debug files somewhere and forget to delete them for years… all of these happen, it’s mostly inevitable.

But, if we’re woken up at 4 A.M. because a /var partition reached 95% utilization, isn’t it true that in most cases the increase was gradual, and the value was already abnormally high — let’s say 93 or 94% — at 4 P.M.?

And wouldn’t it have been much better (for our well-earned rest, among other things) for the person on call to have fixed the problem during the day, before going home?

I thought so, too. Which is why I wrote a script some months ago to detect which servers (from more than a thousand) will need attention soon.

(Looking at that script now, I’m a bit ashamed to share it, as it’s pretty lazily coded, repeating code one time for each filesystem instead of having some kind of function… but it was made in a bit of a hurry some time ago, so because of laziness… I mean, historical accuracy 🙂 I’ll share it as it is (other than translating variable names and output messages from my native Portuguese)).

So, here it is. Don’t laugh too hard, OK? 🙂

#!/bin/bash

# check / partition
ROOT=`df -hl / | tail -1 | awk '{ print $5 }' | cut -d '%' -f 1`
case $ROOT in
    ''|*[!0-9]*) ROOT=`df -hl / | tail -1 | awk '{ print $4 }' | cut -d '%' -f 1` ;;
esac
case $ROOT in
    ''|*[!0-9]*) ROOT=`df -hl / | tail -1 | awk '{ print $3 }' | cut -d '%' -f 1` ;;
esac

TOP=$ROOT
WORST="/"

# check /var partition
VAR=`df -hl /var | tail -1 | awk '{ print $5 }' | cut -d '%' -f 1`
case $VAR in
    ''|*[!0-9]*) VAR=`df -hl /var | tail -1 | awk '{ print $4 }' | cut -d '%' -f 1` ;;
esac

if [ "$VAR" -gt "$TOP" ]; then
        TOP=$VAR
        WORST="/var"
fi

# check /home partition
# comment out this entire block if you don't want to monitor /home
HOME=`df -hl /home | tail -1 | awk '{ print $5 }' | cut -d '%' -f 1`
case $HOME in
    ''|*[!0-9]*) HOME=`df -hl /home | tail -1 | awk '{ print $4 }' | cut -d '%' -f 1` ;;
esac

if [ "$HOME" -gt "$TOP" ]; then
        TOP=$HOME
        WORST="/home"
fi


# check /tmp partition
TMP=`df -hl /tmp | tail -1 | awk '{ print $5 }' | cut -d '%' -f 1`
case $TMP in
    ''|*[!0-9]*) TMP=`df -hl /tmp | tail -1 | awk '{ print $4 }' | cut -d '%' -f 1` ;;
esac

if [ "$TMP" -gt "$TOP" ]; then
        TOP=$TMP
        WORST="/tmp"
fi


# check /opt partition
OPT=`df -hl /opt | tail -1 | awk '{ print $5 }' | cut -d '%' -f 1`
case $OPT in
    ''|*[!0-9]*) OPT=`df -hl /opt | tail -1 | awk '{ print $4 }' | cut -d '%' -f 1` ;;
esac

if [ "$OPT" -gt "$TOP" ]; then
        TOP=$OPT
        WORST="/opt"
fi


#echo "TOP = $TOP"

if [ "$TOP" -ge 70 ] && [ "$TOP" -le 80 ]; then
	echo "Worst partition: ($WORST) at $TOP"
        exit 7
fi


if [ "$TOP" -ge 80 ] && [ "$TOP" -le 90 ]; then
	echo "Worst partition: ($WORST) at $TOP"
        exit 8
fi

if [ "$TOP" -ge 90 ] && [ "$TOP" -le 95 ]; then
	echo "Worst partition: ($WORST) at $TOP"
        exit 9
fi

if [ "$TOP" -ge 95 ] && [ "$TOP" -lt 98 ]; then
	echo "Worst partition: ($WORST) at $TOP"
        exit 10
fi

if [ "$TOP" -eq 98 ]; then
	echo "Worst partition: ($WORST) at $TOP"
        exit 11
fi

if [ "$TOP" -eq 99 ]; then
	echo "Worst partition: ($WORST) at $TOP"
        exit 12
fi


if [ "$TOP" -gt 99 ]; then
	echo "Worst partition: ($WORST) at $TOP :("
        exit 20
fi

echo "Everything OK: worst partition: ($WORST) at $TOP"
exit 0

The goal is to run it on every server you’re responsible for (we use an HP automation tool where I work, but it could be done in many ways, including with a central machine who could ssh “passwordless-ly” into all other servers — it wouldn’t need root access for that, since it doesn’t change anything anywhere. Afterwards, you’re supposed to sort the output by exit codes; anything other than 0 might indicate a problem, and the higher, the worse it is; exit code 20 means a partition at 100%. Again, that HP tool does that sorting easily, but it’s far from being the only way — if you’re reading this, you’ve probably already thought of some.

And then, naturally, you’re supposed to go through the worst cases, either by deleting obvious trash, or by contacting the application teams so that they clean up their stuff.

Depending on your company’s policies, you may want to comment out the block that refers to the /home partition, if that is completely the responsibility of the users.

I don’t have statistics, of course, but I can tell you that being called because of a(n almost) full filesystem, which was relatively frequent a year or so ago, is now extremely rare (only happening when — after work hours — an application goes really wrong (typically because an untested settings change) and starts dumping error messages/debug logs as fast as it can). If only hardware problems didn’t exist, either…

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