Just thought I should do a quick post about a command that is extremely useful but often forgotten and that command is “watch”. Syntax of this command is:
watch[-n SEC] [-t] PROG ARGS
where “n” is the interval in seconds (2 by default).
This command is used as a wrapper, to constantly update results from another command, at a particular frequency. That makes it very useful for monitoring a particular activity for troubleshooting/investigations.
A few months back, I used this command during an investigation into a NTP-related question from a customer. The command used in that case was:
watch “ntpq -p localhost”
If I want to constantly monitor NIC statistics, I can use:
watch “ethtool -S vmnic5”
Another example is while copying large files between datastores. If you want to keep an eye on datastore usage, just in case it fills up, you can use:
watch “df -h”
while the files copy across. This is much more accurate and real-time than the GUI.
I am sure there will be many other uses that you can find for it. This post is just a quick reminder to those who might have forgotten, how useful this command is.
Hope this helps!