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What's a good linux command line utility for watching a log file live? It's probably obvious but I totally forgot it.

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4 Answers 4

up vote 14 down vote accepted

There are two things that leap immediately to mind...

tail -f

or

multitail

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thank you sir. I'll give ya the answer since Linker3000 has so many points, but I still appreciate the help! –  kylehotchkiss Jan 6 '11 at 1:25

Assuming you are in the same folder as the logfile:

tail -f logfilename

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If you want to watch a specific aspect of your file, say just IPs in an access log, you can do :

tail -f your_file | cut -d' ' -f1 | logtop

assuming that IPs are the first column of your log file.

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The tailf command is functionally equivalent to tail -f but better in terms of performance. From man tailf:

tailf will print out the last 10 lines of a file and then wait for the file to grow. It is similar to tail -f but does not access the file when it is not growing. This has the side effect of not updating the access time for the file, so a filesystem flush does not occur periodically when no log activity is happening. tailf is extremely useful for monitoring log files on a laptop when logging is infrequent and the user desires that the hard disk spin down to conserve battery life.

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