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Accepted
Drew Noakes
Asked: 2014-10-29 13:54:38 +0800 CST

Check whether less than some amount of free disk space from the command line

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There are several questions and answers on askubuntu about seeing disk space from the command line.

Naturally, df is the go-to tool for this.

However I want a script at login to raise an alert if the free disk space is below some threshold.

Unfortunately df seems to use arbitrarily sized columns and I'm not sure how to extract just the value from the column I'm interested in.

For example:

$ df /dev/mapper/root
Filesystem       1K-blocks    Used Available Use% Mounted on
/dev/mapper/root   2563092 1649968    763212  69% /
$ df /dev/mapper/root | tail -n 1
/dev/mapper/root   2563092 1649968    763212  69% /
$ df /dev/mapper/root | tail -n 1 | cut -d ' ' -f 9
763212

Really I want the fourth column, yet I must ask for the ninth.

Is there an easier way to either extract the column's value from df's output, or another way altogether to access this value.

command-line

3 Answers

  1. Just realized that this isn't what was asked for, this shows an alert if the space used is greater than a predefined threshold. I'll leave it for further reference though.

    You could use something like the script below

    #!/bin/bash
X=
X=$(du -sc | awk 'NR < 2' | awk '{ print $1 }')
if [ $X -gt 999000 ]; then
  message="Already using `du -sch | awk 'NR <2' |awk '{ print $1 }'` KB"
echo $message | mail -s "File System Full Warning" [email protected]
fi

    X holds the number of KB used, if greater than 999000 it emails a warning message.

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  2. I'd use an awk to only deal with the second line (skips the first here) and get you your column:

    $ df /dev/mapper/sil_acababdfabcf1 | awk 'NR==2 {print $4}'
11903752
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  3. Best Answer

    If you're on Ubuntu 14.04 or later, df can output only the values you want it to:

    $ df --output=avail /
   Avail
15127808

    From man df:

    --output[=FIELD_LIST]
      use the output format defined by FIELD_LIST, or print all fields
      if FIELD_LIST is omitted.
...
FIELD_LIST  is a comma-separated list of columns to be included.  Valid
field names  are:  'source',  'fstype',  'itotal',  'iused',  'iavail',
'ipcent',  'size',  'used',  'avail',  'pcent'  and  'target' (see info
page).

    As noted by Drew Noakes, this ability was added in GNU coreutils 8.21, and so isn't available in older versions of Ubuntu.

    For selecting fields, awk is a far better tool than cut, and you can build on Jan's answer for that after picking the fields you want df to output.

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