04-22-2008
tail | grep lagging badly
I'm trying to use tail/grep to monitor a log file. The command I cooked up is:
tail -n 50 -f output.log | grep 'type:system' | cut -f 5-
A sample line from the log file is:
1208894862 type:system session:0 severity:4 load started
the columns are tab delimited.
this works ok, except that it's inexplicably lagging badly. If I have 2 terminals open, one simply tailing the file and the other tail|greping the file as specified above, it might take 30 seconds or more for the tail|grep terminal to display the next line while the tail terminal displays it instantly.
EDIT: forgot to add this.
Also, sometimes new text does not appear until even more txt is added to the log file.
Example:
'test 1' is written to the log
tail will show this right away, tail | grep will NOT
'test 2' is written to the log
tail will show this right away, tail | grep will show both 'test1' and 'test2' now
Any hints for me? Thanks in advance
Last edited by WasabiVengeance; 04-22-2008 at 05:23 PM..
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TAILF(1) Linux Programmer's Manual TAILF(1)
NAME
tailf - follow the growth of a log file
SYNOPSIS
tailf [OPTION] file
DESCRIPTION
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 peri-
odically 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.
Mandatory arguments to long options are mandatory for short options too.
-n, --lines=N, -N
output the last N lines, instead of the last 10.
AUTHOR
This program was originally written by Rik Faith (faith@acm.org) and may be freely distributed under the terms of the X11/MIT License.
There is ABSOLUTELY NO WARRANTY for this program.
The latest inotify based implementation was written by Karel Zak (kzak@redhat.com).
SEE ALSO
tail(1), less(1)
AVAILABILITY
The tailf command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
13 February 2003 TAILF(1)