Why did this command suddently stop working?

[Red Squirrel]

I got this alert for one of my servers that disk space is -1. Confused, I decided to type the command directly on the server to see why it's returning such as weird value, and now I'm even more confused, because it's returning -869. This is the command:

df -kh / | tail -1 | awk '{ print 100-$4 }'

df -kh returns this:

Filesystem                    Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root  8.5G  7.1G  971M  89% /
tmpfs                         119M     0  119M   0% /dev/shm
/dev/sda1                     485M   33M  427M   8% /boot

The command is suppose to do 100-89 and return the disk space left. It's been working for years, except tonight it randomly stopped. Huh?

Why would it have done this? What's the proper command to get what I want? I don't get why it decided to stop working just now though. Replacing $4 with $5 seems to work... but why? It worked fine before. I can see why it should be 5 because the % is the 5th element... but I'm still confused why it worked before and now it stopped.

OS is CentOS 6.5.

 

[Red Squirrel]

Well it seems to work now that I changed it to 5, but I don't get why it worked for so long with 4. Is there something that can cause the output of df to add an extra column?

 

[KillerBee]

Check yum.log for any recent coreutils update?

or maybe you just need to update coreutils to the latest
if not up2date already


This change was from Oct 2014
https://rhn.redhat.com/errata/RHBA-2014-1457.html

* A recent update of the coreutils packages changed the format of the output from the "df" and "df -k" commands to one line per entry, which is required for POSIX mode. As a consequence, scripts relying on the previous two lines per entry format started to fail. To fix this bug, two-line entries have been reintroduced to the output for modes other than POSIX. As a result, scripts relying on the two-line format no longer fail. (BZ#1057026)

 

[Red Squirrel]

Hmm that explains why it's not consistent between different distros. I don't know why it would have changed on it's own though, does CentOS update automatically? I occasionally go on all my machines and run yum update but have not done it in a while. I probably should now that I think about it. These are not public facing servers so not really that worried either way.

 

[KillerBee]

Hopefully you at least applied the bash update from last year 🙂

 

[Ken g6]

This should work more consistently:

df -kh / | tail -1 | sed -e 's/^.* \([0-9]*\)%.*$/\1/' | awk '{ print 100-$1 }'

There's probably an easier way but I never learned awk.

 

[Red Squirrel]

Hopefully you at least applied the bash update from last year 🙂

Oh that was applied a long time ago. 😛 It's probably been like a month since I ran updates.