How To Use watch Command with Quicker Intervals

watch ifconfig command with 0.2s interval

Sometimes you need to monitor a progress of something in your Linux system - how a file size changes or network traffic gets tracked for a particular interface. There are many scenarios where watch command is handy.

Basic watch command usage

Come up with a command that generates the output you want monitored, and pass this command to watch command as parameters.

For instance, if I run ifconfig wlp2s0, it will give me the current state of the WiFi interface on my XPS laptop:

greys@xps:~$ ifconfig wlp2s0
wlp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.xxx.yyy  netmask 255.255.255.0  broadcast 192.168.xxx.255
        inet6 fe80::af47:a73c:a73c:66b4  prefixlen 64  scopeid 0x20<link>
        ether 9c:b6:d0:97:d0:a7  txqueuelen 1000  (Ethernet)
        RX packets 562709  bytes 402837160 (384.1 MiB)
        RX errors 0  dropped 1956  overruns 0  frame 0
        TX packets 95351  bytes 15925207 (15.1 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

As you can see, some parameters are counters - RX packets and bytes, TX packets and bytes. So if you want to watch how they’re updated in nearly real time, you can use watch command:

greys@xps:~$ watch ifconfig -a

By default watch command uses interval of 2sec - meaning it will refresh output every 2 seconds by re-running the same command you specified.

It will look like this:

Every 2.0s: ifconfig wlp2s0                                                                xps: Sat Jul 17 20:40:00 2020

wlp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.xxx.yyy  netmask 255.255.255.0  broadcast 192.168.xxx.255
        inet6 fe80::af47:a73c:a73c:66b4  prefixlen 64  scopeid 0x20<link>
        ether 9c:b6:d0:97:d0:a7  txqueuelen 1000  (Ethernet)
        RX packets 614256  bytes 435424196 (415.2 MiB)
        RX errors 0  dropped 2142  overruns 0  frame 0
        TX packets 106700  bytes 17857828 (17.0 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Quicker Intervals for watch command

A friend reminded me the other day, that in Linux it’s actually possible to make watch command wait a lot less between re-runs of the commands you pass to it. You can go as far as making watch re-run every 0.1s, but even 0.2s is going to be 10x better than default - so the counters in my example will now be updating almost instantly.

Just use the -n parameter to specify new time interval:

greys@xps:~$ watch -n0.2 ifconfig wlp2s0

Notice how it says Every 0.2s now at the top left corner:

Every 0.2s: ifconfig wlp2s0                                                                xps: Sat Jul 17 20:55:00 2020

wlp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.xxx.yyy netmask 255.255.255.0  broadcast 192.168.xxx.255
        inet6 fe80::af47:a73c:a73c:66b4  prefixlen 64  scopeid 0x20<link>
        ether 9c:b6:d0:97:d0:a7  txqueuelen 1000  (Ethernet)
        RX packets 621467  bytes 437892389 (417.6 MiB)
        RX errors 0  dropped 2156  overruns 0  frame 0
        TX packets 107731  bytes 18036913 (17.2 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

See Also

• Basic Unix Commands
• Advanced Unix Commands