ubuntu 18.04 server

You may know tail -f, but here is a tool specifically designed to navigate through log files: lnav.

Viewing a changing log file

tail -f logfile will wait for output of a log file, and your favorite editor may warn you about a file change.

lnav logfile will handle log file change.

logrotate

Most Linux distribution use logrotate to handle log files rotation. The goal is to rotate logs when they are too big, or too old. The shortcoming is that it creates multiples log files, in various formats, with funny names.

syslog becomes syslog.1 then syslog.1.gz, syslog.2.gz, …

lnav -r /var/log/syslog will open /var/log/syslog, and all rotated files!

Multiple log files

lnav will display multiple log files in the same view (log entries sorted by time).

Example : lnav -r /var/log/syslog /var/log/auth.log

Shortcuts

A complete list of hotkeys is available here, but here are some I use everyday:

Navigation

Key	effect
Home or g	Top of the view
End or G	Bottom of the view
PgDn or space	Down a page
PgUp or b	Up a page
e/E	Next/previous error
w/W	Next/previous warning
f/F	Next/previous file

Searching

Key	effect
/	Search for lines matching a regular expression
CTRL+]	Abort
n/N	Next/previous hit

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Question, remark, bug? Don't hesitate to contact me or report a bug.