May the source be with you, but remember the KISS principle ;-)

Contents Bulletin Scripting in shell and Perl Network troubleshooting History Humor



See also

Recommended Links Recommended Papers Static pattern matching Log Colorizing
Logrep devialog Swatch Kazimir LooperNG Logwatch
Splunk Sawmill Lire Epylog MultiTail Net::Dev::
Http logs analyzers Perl-based tools Multipurpose plug-in based analyzers Event correlation Humor Etc

In Red Hat and Suse log rotation  it is handled by the logrotate utility and configured using files in /etc/logrotate.d.

By default, logs are kept for 4 weeks. 

To change the time your logs are kept for, edit /etc/logrotate.conf and change the rotate parameter.  You can also override this for specific logs by editing the files in /etc/log/logrotate.d/.  For more details see the logrotate man page.

If you have more that one Linux/Unix server then you should probably set one machine up as a log server and send all your logs to a central machine as well as storing them locally.  This makes is easier to process your logs and means you have a second copy should a machine have it's security compromised.

To make a server accept log messages from other machines you need to enable syslog remote reception.  This can be done by editing /etc/sysconfig/syslog and adding "-r" to the SYSLOGD_OPTIONS so it looks like this


Then restart syslog by doing

# /etc/rc.d/init.d/syslog restart

You should see a message in the log files about remote reception

To make a machine send it's log messages to your log server you need to add an entry to /etc/syslog.conf.  Something like

*.info @loghost

should be all that is needed.  See the man page for more details (man 5 syslog.conf)

You also need to restart syslog after this change.  The procedure is the same as above.

Restricting Access

Using tcp wrappers is restrict access is simple to set up.  Most services are already configured to use tcp wrappers.  The most secure way to configure tcpwrappers is to deny everything be default.

/etc/hosts.deny should contain only the line


Then you can add services to /etc/hosts.allow as appropriate.  For example

swat: 192.168.5. : severity notice
sshd: KNOWN : severity notice
ALL: LOCAL : severity notice

You do not need to restart anything after changing these files.  They are reread every time a connection is made.

 Following are a few points of interest in the logrotate tour:

/usr/sbin/logrotate -- Utility residence
/etc/logrotate.conf -- Default configuration file
/etc/logrotate.d -- Default directory for other configuration files
/var/lib/logrotate.status -- Default state file

On RH, logrotate is run from a daily job directory /etc/cron.daily/logrotate. When logrotate is called, it obtains information about which files it is processing by using the default configuration file /etc/logrotate.conf. Alternate configuration files can be used if optioned. The configuration file defines the file to rotate and the parameters to apply. A configuration file entry may look like this:

"/var/log/logfile.log" {
        rotate 7
Using the configuration shown here, the file logfile.log would be compressed and rotated and given the name of logfile.log.1.gz. After day two, the file logfile.log.1.gz would be rotated to logfile.log.2.gz and new copy of logfile.log.1.gz produced from logfile.log. At the end of the configuration file schedule, the directory would contain seven copies of the database. On the eighth day, the copy with the extension logfile.log.7.gz would be replaced with another rotated copy. A long listing (ls -al) in the directory would display seven copies of the database files, with dates preserved from when they were first created.

The man pages for logrotate explain the parameters used to control logrotate. The remainder of this article describes how logrotate can be used to produce a backup schema.

When planning the backup process, I used a variation on the grandfather-father-son backup tape rotation method. The backup set consists of grandfather(monthly), father(weekly), and son(daily) as shown in Figure 1.

Under this grandfather-father-son implementation method, a full backup is performed every day (Monday-Sunday); a full backup of the oldest daily is preserved every Sunday; a full backup of the oldest weekly is preserved the last day of a four-week cycle. This assumes you start the daily cycle on a Monday. After 1 year, 6 dailies, 3 weeklies, and 12 monthly copies are preserved.

Logrotate works similarly to a stack in programming. As each file is rotated, it is pushed onto the stack and forces other files down the stack. The size of the stack is determined by the rotate value in the logrotate configuration file. Once the stack capacity is reached, the first file in gets pushed out. Figure 1 illustrates the idea.

To produce the backup schema shown in Figure 1, create the configuration file /etc/logrotate_backup.conf from the following listing:

#Description:script designed to produce backups
#Author: Sean D. Conway
#Wed Aug 28 18:12:59 CDT 2002
#replace the path to be backed up.
#don't remove "" good for files that have spaces.
#maintain the "." file extensions this will preserve the frequency

#daily (son)
"/home/oracle/backup/database" {
        rotate 7

#weekly (father)
"/home/oracle/backup/database.7.gz" {
        rotate 4

#monthly (grandfather)
"/home/oracle/backup/database.7.gz.4" {
        rotate 12
This configuration file is divided into three sections: daily, weekly, and monthly. The following listing provides some comments to explain the parameter lines found in the script:
#daily (son)                         <--comments line
"/home/oracle/backup/database" {     <--file to rotate
        daily                        <--rotation schedule
        rotate 7                     <--rotation interval
        compress                     <--compress the file
The parameters here enable the logrotate program to rotate and compress daily a file called database. The rotation interval is seven. At the end of one week, the storage directory will contain the following files: database.1.gz, database.2.gz, database.3.gz, database.4.gz, database.5.gz, and database.6.gz. The weekly configuration would rotate the file database.7.gz to database.7.gz.1. The file database.1.gz would be the most current.

The logrotate utility can access the configuration files using two methods:

1. The configuration file can be placed in the default configuration file directory /etc/logrotate.d. This directory is listed in logrotates default configuration file /etc/logrotate.conf. All files in /etc/logrotate.d are additional configuration files that will be processed by the program.

2. An alternate method is to force the logrotate program to use an alternate configuration file from a command line. The following is the cron entry to support logrotate running each day at 07:00 using a configuration file called /etc/logrotate_backup.conf.

00 07 * * * /usr/sbin/logrotate -f /etc/logrotate_backup.conf
I prefer the second method because it allows more flexible scheduling.

The logrotate backup mechanism is used to support three database servers as shown in Figure 2. Each database server produces a backup file and sends it to a server called a tape_gate. On the tape_gate server, logrotate runs daily and takes care of producing the rotation schema. The complete backup series is exported to tape for offsite storage.

Tape_gate also runs a licensed tape client for accessing the tape silo. This configuration allows the administrators to use the client software to schedule and access the backups. The administrator can use the backups stored locally or pull the file back from the tape storage device. All the file creation dates are preserved, and a simple grep on a month name will produce a list of backup files available for that month.

To get support for this backup solution, I had to address some design limitations. This implementation requires a server to process the backups. The horsepower required for the server is minimal. For this installation, I used a reclaimed Pentium desktop with an additional cost of two hard drives. It does provide an alternate point for accessing backups. I find it easier to access a backup from a disk rather than searching a tape library.

Backup files are moved from the source to tape_gate using secure ftp. At selective network slow periods the additional network traffic is acceptable. Secure ftp provides access to a ready backup from tape_gate if needed.

Table 1 shows the complete set of filenames after a one-year cycle. The drive capacity must be sufficient to support the number of system backups being handled. The cost for hard drive capacity today is lower than it was ten years ago. Sixty-gig IDE drives are common. At 14-MB compressed, I was able to get all the backups on a 60-GB drive. The three-database server backups total 500 MB compressed.

The feature that sold this design was cost. A client license for accessing the tape silo costs $1200. Each of the databases runs a different operating system, so each would have needed a different client license. Instead, two drives cost $300 and $1200 for one client license for tape_gate; I saved $2100.

The alternative was to create NFS mount on all the servers.

I have been asked to add additional backups to the server. It seems this common approach to backups for a variety of systems can make life easier for administrators. Certainly, one common backup mechanism for all systems is easier to remember than a different backup method for each system.

Sean D. Conway is a former college instructor turned Network System Specialist for a regional telecommunications company in Canada. Working with administrators, they are responsible for the care and feeding of operational support systems inside the telecommunication cloud. He still dabbles in network theory lectures. His formal electronic engineering technology training and education background are valuable tools in achieving a goal -- making learning about computers and networks easier.



Old News  ;-)

Rotating Linux Log Files MDLog-sysadmin

Comments Chris Riney - June 7, 2006

Iím glad that he mentioned that this was based on a Debian systems, since the RedHat & SuSE systems that I work with do not have the syslog ďFeatureĒ that is described (must be part of syslogNG which Iím not familiar with). Both of these major commercial distributions manage the syslog files via logrotate.

Actually Iím just starting to work with SuSE Enterprise, and Iím noticing the differences in the way RedHat & SuSE implement scheduling Hourly, Daily, Weekly, & Monthly rotations.

A feature of of LogRotate 3.7.x that I found, (and was looking for) is the Ďdateextí which appends the rotation date to the end instead of a sequential number. The problem I have with the sequential number, is that logrotate moves the older logís up the sequence, which causes those file to be backed-up multiple times with differential backups.

One item that you didnít cover, is how logrotate knows when it is the proper time to rotate a daily, weekly, or monthly file. Part of that is controlled by the status file (/var/lib/logrotate.status on most Linux system) which tracks when a particular file was last rotated. The other part is that Monthly rotations are done with the first run of logrotate that month, and Weeklyís are run if the last run was later in the previous week, or the last rotation was over 7 days prior (Sunday=0 Saturday=6). So if you are running logrotate daily, then it works itself out to the first day of the month, and Sundayís for the weeklies.

logrotate notes on usage

These are my personal notes on how to use `logrotate' on a linux system.
I'm writing these notes to help me make sense of how things work.

2005-5-5: I don't know where the logrotate source went to. All of my links to logrotate are broken. The source in about September 2001 was logrotate-3.3.tar.gz. That probably isn't very useful though.

How logrotate is invoked from cron.

On one of my RedHat 5.2 systems, `crond' is started from the script /etc/rc.d/init.d/crond. The manual `man cron' says that cron

searches for /etc/crontab and the files in the /etc/cron.d/ directory.

My /etc/crontab file contains the following.


# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
0  0 1 * * root run-parts /etc/cron.monthly
And the /etc/cron.d directory contains nothing.

So clearly, any logrotate commands are being run out of one or more of the /etc/cron.* files. The manual `man 5 crontab' indicates that the above commands mean that the program `run-parts' will be run as user `root' for each of the scripts.

The command `run-parts' turns out to be the script /usr/bin/run-parts, which is very short, as follows.


# run-parts - concept taken from Debian

# keep going when something fails
set +e

if [ $# -lt 1 ]; then
        echo "Usage: run-parts <dir>"
        exit 1

if [ ! -d $1 ]; then
        echo "Not a directory: $1"
        exit 1

for i in $1/* ; do
        [ -d $i ] && continue
        if [ -x $i ]; then

exit 0
In essence, this just runs all of the scripts in the specified directory. E.g. each hour, the executable plain files in /etc/cron.hourly are run.

It turns out that the `logrotate' program is invoked from /etc/cron.daily. This is the contents of the file /etc/cron.daily/logrotate.


/usr/sbin/logrotate /etc/logrotate.conf
This means that the only file that `logrotate' gets its instructions from directly is /etc/logrotate.conf, which contains the following lines.
# see "man logrotate" for details
# rotate log files weekly

# keep 8 weeks worth of backlogs
rotate 8

# send errors to root
errors root

# create new (empty) log files after rotating old ones

# uncomment this if you want your log files compressed

# RPM packages drop log rotation information into this directory
include /etc/logrotate.d

# no packages own lastlog or wtmp -- we'll rotate them here
/var/log/wtmp {
    rotate 1

# system-specific logs may be configured here
This is all explained in the manual `man logrotate'.

Operation of logrotate.

The directory /etc/logrotate.d contains the following files.

-rw-r--r--   1 root     root          354 Oct 13  1998 apache
-rw-r--r--   1 root     root          108 Aug 28  1999 cron
-rw-r--r--   1 root     root          188 Oct 14  1998 linuxconf
-rw-r--r--   1 root     root          156 Oct 13  1998 mgetty
-rw-r--r--   1 root     root          327 Aug 12  1998 syslog
-rw-r--r--   1 root     root          457 Sep 10  1998 uucp
The file /etc/logrotate.d/apache is the one I'm interested in for this exercise. This file contains the following.
/var/log/httpd/access_log {
        /usr/bin/killall -HUP httpd

/var/log/httpd/agent_log {
        /usr/bin/killall -HUP httpd

/var/log/httpd/error_log {
        /usr/bin/killall -HUP httpd

/var/log/httpd/referer_log {
        /usr/bin/killall -HUP httpd
When I installed the latest version of Apache to get the PHP3 and PostgreSQL to work (around 20 March 2000) on my web server machine, I installed Apache so that the log files were in /home2/apache/logs instead of /var/log/httpd.

Therefore what I need to do now is to modify the /etc/logrotate.d/apache file so that the files referred to are all in the directory /home2/apache/logs instead. My new /etc/logrotate.d/apache script is as follows, and I saved the old one in directory /etc/logrotate.d/old1.

# The new improved logrotate script for apache on fox.

/home2/apache/logs/*-access_log {
    rotate 9
    olddir /home2/apache/logs/oldlogs
        /usr/bin/killall -HUP httpd

/home2/apache/logs/*-combref_log {
    rotate 9
    olddir /home2/apache/logs/oldlogs
        /usr/bin/killall -HUP httpd

/home2/apache/logs/*-error_log {
    rotate 9
    olddir /home2/apache/logs/oldlogs
        /usr/bin/killall -HUP httpd

For a log file of an ad-hoc utility I wrote, I have now created this configuration file /etc/logrotate.d/dping for `logrotate'.

# The new improved logrotate script for dping on fox.

/var/log/dping.txt {
    rotate 9
#    delaycompress
Since the creating process cannot be HUPped to make it work with a new log file, I've used `copytruncate' to copy the file and then truncate it. The `delaycompress' is not useful because the original log file is copied rather than moved. Creation of .cvsignore file

Now on Sunday 30 September 2001, it's time to get `logrotate' going on my new SuSE 7.1 web server `dog'. The problem is that SuSE 7.1 does not come with logrotate software on it. So I had to go and look for it. The link at redhat was wrong, but by looking around a bit, I finally found it at I downloaded this file: logrotate-3.3.tar.gz.
[2005-5-5: I think it has disappeared again now. But here's a backup copy of logrotate-3.3.tar.gz.]
This can be compiled very simply with `make' and `make install'. There's a manual logrotate.8 with it too. The binary is installed as /usr/sbin/logrotate. So now all I have to do is write a configuration file for the logrotate program and then write a cron script for it.

(Note that since my main initial consideration is to rotate the httpd logs for the beginning of October 2001, I could just use the Apache tool for this purpose, which is /usr/local/apache/bin/rotatelogs on my system. However, I can't understand the documentation for this. So I'm playing safe and using the more flexible redhat `logrotate' tool instead.)

On my SuSE 7.1 machine `dog', the manual says that after reading the per-user crontab files in /var/spool/cron/tabs on start-up, the cron process reads the file /etc/crontab. On my machine as configured, I find the following.

root@dog# more /etc/crontab

#-* * * * *    root  test -x /usr/sbin/atrun && /usr/sbin/atrun
0 21 * * *     root  test -x /usr/sbin/faxqclean && /usr/sbin/faxqclean
5 22 * * *     root  test -x /usr/sbin/texpire && /usr/sbin/texpire
25 23 * * *    root  test -e /usr/sbin/faxcron && sh /usr/sbin/faxcron | mail FaxMaster

# check scripts in cron.hourly, cron.daily, cron.weekly, and cron.monthly
-*/15 * * * *   root  test -x /usr/lib/cron/run-crons && /usr/lib/cron/run-crons
59 *  * * *     root  rm -f /var/spool/cron/lastrun/cron.hourly
14 0  * * *     root  rm -f /var/spool/cron/lastrun/cron.daily
29 0  * * 6     root  rm -f /var/spool/cron/lastrun/cron.weekly
44 0  1 * *     root  rm -f /var/spool/cron/lastrun/cron.monthly
There's nothing here to help me with initiating my daily script. (By the way, the fax commands are a bit worrying. I'll get rid of those when I understand exactly what they do. They obviously produce many meaningless message which root receives every day!)

So my next step is to look at the files in /etc/cron.d, because the cron manual says that all scripts in this directory are read next. On my machine the only file in /etc/cron.d is a script `seccheck', which produces copious useless messages to root every day and week. (I'll see if I can get rid of that some day too!)

The directory /etc/cron.daily contains a script `aaa_base_rotate_logs' which contains a complex set of rotation rules, but how are the scripts in this directory invoked? Hmmm... Maybe they're invoked from that `/usr/lib/cron/run-crons' script. Yes!! That's where it's invoked from. Yet another big, incomprehensible script. The core of that script is the following Bourne-shell loop.

for CRONDIR in /etc/cron.{hourly,daily,weekly,monthly} ; do
    test -d $CRONDIR || continue
    test -e $SPOOL/$BASE && {
        case $BASE in
          cron.hourly)  TIME="-cmin  +60 -or -cmin  60" ;;
          cron.daily)   TIME="-ctime +1  -or -ctime 1"  ;;
          cron.weekly)  TIME="-ctime +7  -or -ctime 7"  ;;
          cron.monthly) TIME="-ctime +`date -u +%d`"    ;;
        eval find $SPOOL/$BASE $TIME | xargs -r rm -f
    if test ! -e $SPOOL/$BASE ; then
        touch $SPOOL/$BASE

        # keep going when something fails
        set +e
        for SCRIPT in $CRONDIR/*[^~,] ; do
            test -d $SCRIPT && continue
            test -x $SCRIPT || continue
           case "$SCRIPT" in
               *.rpm*)         continue ;;
               *.swap)         continue ;;
               *.bak)          continue ;;
               *.orig)         continue ;;
               \#*)            continue ;;
           /sbin/checkproc $SCRIPT && continue
           nice -15 $SCRIPT
Now what does this mean?
The command `BASE=${CRONDIR##*/}' means that BASE is set to the `longest substring of $CRONDIR which matches pattern "*/"', according to my Bash reference card. This just means that the leading path components are removed. (This is done more simply in C-shell!) In the case of the daily cron job, if there is a file /var/spool/cron/lastrun/cron.daily (which is true), then the following command is run.
eval find /var/spool/cron/lastrun/cron.daily -ctime +1 -or -ctime 1 | xargs -r rm -f
The `xargs' command (which I have never seen before) builds and executes a command line from standard input. Weird! The `xargs' manual says this.
If  the  standard  input  does not contain any non-blanks,
do not run the command.  Normally, the command is run once
even if there is no input.
So in this case, the command `rm -f' is executed for each of the files with modification times within 24 hours of the current time. I don't really understand this.

It looks like the file removal commands in the file /etc/crontab are designed to synchronise the operation of the quarter-hour operations. The commands are only executed if the files in /var/spool/cron/lastrun have been removed. What a convoluted way of achieving a simple objective!!

Next any file in the directory /etc/cron.daily which do not end in the characters `~' or `,' (presumed to be edited files) are executed if they are executable and do not have the endings .rpm, .swap, .bak or .orig as follows.

           /sbin/checkproc $SCRIPT && continue
           nice -15 $SCRIPT
The loop continues is the process is already running. Otherwise it is run with nice level 15.

What this all means finally is that any script in the directory /etc/cron.daily will be run at 00:00 on each day. More to the point, the /etc/cron.monthly scripts are run at 00:00 at the beginning of each month. It all looks a bit dodgy because the `date' test is `date -u', which gives the current UTC day. But this should work, although the motivation for the `-u' is not quite clear.

All I have to do now is write a script and put it in /etc/cron.monthly. No problem!


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