Check Available Disk Space and Notify

Here's some handy bash script to notfiy support when we are running low on disk space.

#!/bin/bash
#
# Description:Checks the available space for the disk mounted as / (root)
#             If disk space is less than 10GB it will send out a notification
#

# Send emails to these people
EMAILID=support@mydomain.com

# Min Free Space
MINSPACE=10485760

# Get the space available
FREESPACE=`df / | awk '{ if( NR == 2) print $4 }'`

# Send email if required
if [ $FREESPACE -le $MINSPACE ];
then
 logger "Warning: Root Drive Running Out Of Disk Space [${FREESPACE}KB]"
 mail -s 'My Favourite Production Server Disk Space' ${EMAILID} << EOF
My Favourite Production server root drive is running out of disk space. Current free space is ${FREESPACE} KB @ $(date)
EOF
fi

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Truncate a file

While setting up Apache HTTP Server to rotate logs I came across an interesting problem. How would you truncate a file? The trivial solution that I came up with was

[root@lambda ~]# rm -f /var/log/httpd/foo.log
[root@lambda ~]# touch /var/log/httpd/foo.log

Unfortunately this doesn't work. The HTTP Server ceases logging to the file unless there is a server restart. After prying around the web I came across some interesting tricks but the one that stood out was:

[root@lambda ~]# :> /var/log/httpd/foo.log

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TCP Dump

A very convenient way to find out traffic content on a particular port.

tcpdump -l -i eth0 -w - src or dst port 3306 | strings

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