Common Linux log files name and usage--reference

In the following example,you can view the content of var/log/cron from line number 101 to 110.M – Starting line numberN – Ending line number<div class="block-panel">
Syntax: sed -n M,Np FILENAME$ sed -n 101,110p /var/log/cron

Example 2: Display first N lines of a file using head commandThis example displays only first 15 lines of /var/log/maillog file. Change 15 to 10 to display the first 10 lines of a log file.?<div class="block-panel">
Syntax:?head -n N FILENAME$ head -n 15 /var/log/maillog

Example 3: Ignore last N lines of a file using head commandThis example shows how to ignore the last N lines,and show only the remaining lines from the top of file. The following example will display all the lines of the /var/log/secure except the last 250 lines.<div class="block-panel">
Syntax:?head -n -N FILENAME$ head -n -250 /var/log/secure

Example 4: Display last N lines of the file using tail commandThis example displays only last 50 lines of /var/log/messages file. Change 50 to 100 to display the last 100 lines of the log file.<div class="block-panel">
Syntax:?tail -n N FILENAME$ tail -n 50 /var/log/messages

Example 5: Ignore first N-1 lines of the file using tail commandThis example shows how to ignore the first N-1 lines and show only the remaining of the lines. The following example ignores the 1st four lines of the /etc/xinetd.conf,which contains only the comments.<div class="block-panel">
Syntax:?tail -n +N FILENAME$ tail -n +5 /etc/xinetd.conf?defaults{instances = 60log_type = SYSLOG authprivlog_on_success = HOST PIDlog_on_failure = HOSTcps = 25 30}includedir /etc/xinetd.d

Example 6: View growing log file in real time using tail commandThis is probably one of the most used command by sysadmins.To view a growing log file and see only the newer contents use tail -f as shown below.The following example shows the content of the /var/log/syslog command in real-time.<div class="block-panel">
Syntax:?tail -f FILENAME$ tail -f /var/log/syslog

Example 7: Display specific lines (based on line number) of a file using head and tail commandThe example below will display line numbers 101 – 110 of /var/log/anaconda.log fileM – Starting line numberN – Ending line number<div class="block-panel">
Syntax:?cat file | tail -n +N | head -n (M-N+1)$ cat /var/log/anaconda.log | tail -n +101 | head -n10

cat : prints the whole file to the stdout.tail -n +101 : ignores lines upto the given line number,and then start printing lines after the given number.head -n 10 : prints the first 10 line,that is 101 to 110 and ignores the remaining lines.Example 8: Display lines matching a pattern,and few lines following the match.The following example displays the line that matches “Initializing CPU” from the /var/log/dmesg and 5 lines immediately after this match.<div class="block-panel">
# grep "Initializing CPU#1" /var/log/dmesgInitializing CPU#1[Note: The above shows only the line matching the pattern]# grep -A 5 "Initializing CPU#1" dmesgInitializing CPU#1Calibrating delay using timer specific routine.. 3989.96 BogoMIPS (lpj=1994982)CPU: After generic identify,caps: bfebfbff 20100000 00000000 00000000CPU: After vendor identify,caps: bfebfbff 20100000 00000000 00000000monitor/mwait feature present.CPU: L1 I cache: 32K,L1 D cache: 32K

[Note: The above shows the line and 5 lines after the pattern matching]Example 9: Displaying specific bytes from a file.The following example explains how to display either the top 40 or the last 30 bytes of a file.<div class="block-panel">Display first 40 bytes from syslog.$ head -c40 /var/log/syslog

<div class="block-panel">Display last 30 bytes from syslog.$ tail -c30 /var/log/syslog

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