日誌輪轉特別適用於具有固定檔名的日誌檔案，比如MySQL的出錯日誌、常規查詢日誌、慢查詢日誌等。Linux系統有一個非常好用的根據logratate可以實現自動輪轉，本文介紹它的原理和用法。

預設情況下，logrotate部署為每天執行的cron job，你可以在目錄/etc/cron.daily裡找到名為logrotate的配置檔案。那麼它是在每天的上面時候執行的呢？開啟檔案/etc/crontab就知道了，下面是我機器上的情況：

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# 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
42 4 1 * * root run-parts /etc/cron.monthly
 

從上面的配置我們可以知道，/etc/cron.daily是在每天凌晨4:02執行。也就是說，每天4:02分/etc/cron.daily/logrotate將會自動執行，下面是它的內容：

#!/bin/sh

/usr/sbin/logrotate /etc/logrotate.conf
EXITVALUE=$?
if [ $EXITVALUE != 0 ]; then
    /usr/bin/logger -t logrotate "ALERT exited abnormally with [$EXITVALUE]"
fi
exit 0

從上面我們可以知道，logratate預設的配置檔案是/etc/logratate.conf，下面是它的內容：

EXITVALUE=$?
if [ $EXITVALUE != 0 ]; then
    /usr/bin/logger -t logrotate "ALERT exited abnormally with [$EXITVALUE]"
fi
exit 0
[
 
[email protected] /etc/cron.daily ]# cat /etc/logrotate.conf
# see "man logrotate" for details
# rotate log files weekly
weekly

# keep 4 weeks worth of backlogs
rotate 4

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

# uncomment this if you want your log files compressed
#compress

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

# no packages own wtmp -- we'll rotate them here
/var/log/wtmp {
    monthly
    minsize 1M
    create 0664 root utmp
    rotate 1
}

/var/log/btmp {
    missingok
    monthly
    minsize 1M
    create 0600 root utmp
    rotate 1
}
 

從上面我們可以知道，這個預設的配置檔案將讀取目錄/etc/logrotate.d，所以我們只要把自己寫的配置檔案放到該目錄下即可。

MySQL本省提供了一個rotate的參考配置檔案，在support-files目錄下，檔名為mysql-log-rotate，內容如下：

# This logname can be set in /etc/my.cnf
# by setting the variable "err-log"
# in the [safe_mysqld] section as follows:
#
# [safe_mysqld]
# err-log=/opt/mysql/data/mysqld.log
#
# If the root user has a password you have to create a
# /root/.my.cnf configuration file with the following
# content:
#
# [mysqladmin]
# password = <secret>
# user= root
#
# where "<secret>" is the password.
#
# ATTENTION: This /root/.my.cnf should be readable ONLY
# for root !

/opt/mysql/data/mysqld.log {
        # create 600 mysql mysql
        notifempty
        daily
        rotate 3
        missingok
        compress
    postrotate
        # just if mysqld is really running
        if test -x /opt/mysql/bin/mysqladmin && \
           /opt/mysql/bin/mysqladmin ping &>/dev/null
        then
           /opt/mysql/bin/mysqladmin flush-logs
        fi
    endscript
}

logrotate常見選項:

選項	含義
compress	壓縮日誌檔案的所有非當前版本
copy	複製當前的日誌檔案,忽略create引數
copytruncate	複製當前的日誌檔案,並置空當前檔案
daily	每天輪日誌檔案i
dateext	輪換的日誌字尾為-YYYYMMDD格式
delaycompress	壓縮除了當前和最近之外的所有其他版本
missingok	如果日誌不存在,不會報錯
notifempty	如果日誌為空,則不輪換
rotate n	在輪換方案中包含n個版本的日誌
size=logsize	如果日誌檔案大於logsize才輪換

我們只要根據自己的需要，修改相應配置即可，下面是一個例子：

1）建立MySQL root密碼檔案

vi /root/.my.cnf

[mysqladmin]
password = ***
user= root

chmod 600 /root/.my.cnf
2）把mysql-log-rotate拷貝至/etc/logrotate.d目錄下，修改其內容為：

/data/mysql/log/slow.log
/data/mysql/log/alert.log {
        create 600 mysql mysql
        notifempty
        daily
        rotate 7
        missingok
        # compress
    postrotate
        # just if mysqld is really running
        if test -x /opt/mysql/bin/mysqladmin && \
           /opt/mysql/bin/mysqladmin ping &>/dev/null
        then
           /opt/mysql/bin/mysqladmin flush-logs
        fi
    endscript
}

3）執行以下命令測試

/usr/sbin/logrotate -f /etc/logrotate.d/mysql-log-rotate