log tips and tricks

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As engineers we’re constantly trawling through logs. Here’s some tips for making that task a little easier.

Searching logs

For larger logs we may want to scroll by page:

cat mylog.log | less

We can then use PgUp or PgDn or the mac equivalent.

Regex search in less

/<regex>

Find error with grep

$ grep -I error /var/log/messages or find firewall related stuff

sudo tail -f /var/log/messages |grep FIREWALL

Some common NGINX searches

$ grep "/login.php??" /var/log/nginx/access.log
$ grep "...etc/passwd" /var/log/nginx/access.log
$ egrep -i "denied|error|warn" /var/log/nginx/error.log

$ sudo grep 404 /var/log/nginx/access.log
$ sudo grep "GET /images/cityscience.jpg" /var/log/nginx/access.log
$ sudo grep -i "get /images/cityscience.jpg" /var/log/nginx/access.log

$ sudo tail -n 100 /var/log/nginx.log | grep 404

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