Logrotate是一个日志文件管理工具。用来把旧文件轮转、压缩、删除，并且创建新的日志文件。我们可以根据日志文件的大小、天数等来转储，便于对日志文件管理，一般都是通过cron计划任务来完成的。
安装
# yum install logrotate cron
文件位置
- 默认状态文件在
/var/lib/logrotate.status - 默认配置文件是
/etc/logrotate.conf
运行原理
Logrotate是基于CRON来运行的，其脚本在/etc/cron.daily/logrotate
#!/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
实际运行时，Logrotate会调用配置文件/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
# use date as a suffix of the rotated file
dateext
# 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 and btmp -- we'll rotate them here
/var/log/wtmp {
monthly
create 0664 root utmp
minsize 1M
rotate 1
}
/var/log/btmp {
missingok
monthly
create 0600 root utmp
rotate 1
}
# system-specific logs may be also be configured here.
这里的设置是global attribute，而在/etc/logrotate.d目录里，可以定义每项应用服务的配置文件，并且定义会覆盖当下。
定时执行/etc/cron.daily目录下的文件的设置，则在/etc/anacrontab里定义的
# /etc/anacrontab: configuration file for anacron
# See anacron(8) and anacrontab(5) for details.
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# the maximal random delay added to the base delay of the jobs
RANDOM_DELAY=45
# the jobs will be started during the following hours only
START_HOURS_RANGE=3-22
#period in days delay in minutes job-identifier command
1 5 cron.daily nice run-parts /etc/cron.daily
7 25 cron.weekly nice run-parts /etc/cron.weekly
@monthly 45 cron.monthly nice run-parts /etc/cron.monthly
关于anacrontab，这里不做介绍。
命令参数
Usage: logrotate [OPTION...] <configfile>
-d, --debug Don't do anything, just test (implies -v)
-f, --force Force file rotation
-m, --mail=command Command to send mail (instead of `/bin/mail')
-s, --state=statefile Path of state file
-v, --verbose Display messages during rotation
--version Display version information
Help options:
-?, --help Show this help message
--usage Display brief usage message
配置参数
-
compress使用gzip来压缩日志文件 -
nocompress日志不压缩的参数 -
compresscmd指定压缩工具，默认gzip -
uncompresscmd指定解压工具，默认gunzip -
delaycompress推迟要压缩的文件，直到下一轮询周期再执行压缩，可与compress搭配使用 -
dateext轮询的文件名字带有日期信息 -
dateformat格式化归档日期后缀，只有%Y,%m,%d和%s -
daily日志按天轮询 -
weekly日志按周轮询 -
monthly日志按月轮询 -
yearly日志按年轮询日志，不关注 -
maxage count删除count天前的轮询日志文件 -
rotate count删除count个外的轮询日志文件 -
notifempty文件为空时，不进行轮询 -
size size日志文件根据大小规定进行轮询，默认单位是byte，也可指定kb, M, G；So size 100, size 100k, size 100M and size 100G are all valid. -
minsize size文件大小超过size后才能进行轮询，此时会略过时间参数 -
postrotate/endscript在所有其它指令完成后，postrotate和endscript里面指定的命令将被执行。 -
sharedscripts在所有的日志文件都轮询完毕后统一执行一次脚本。当声明日志文件的时候使用通配符时需要用到 -
olddir指定轮询后的日志文件存放在directory，必须和当前日志文件在同一个文件系统 -
create mode owner group新日志文件的权限，属主属组
配置参数只列出较为常用的
测试
测试以日志大小为规定的轮询，创建个15M大小的日志文件
# head -c 15M /dev/urandom > /var/log/will-log
设置配置文件
# vim /etc/logrotate.d/will-log
/var/log/will-log {
compress
delaycompress
missingok
notifempty
daily
rotate 7
size 10M
olddir /tmp
dateext
create 0644 root root
}
debug验证下
# logrotate -d /etc/logrotate.d/will-log
reading config file /etc/logrotate.d/will-log
olddir is now /tmp
Handling 1 logs
rotating pattern: /var/log/will-log 10485760 bytes (7 rotations)
olddir is /tmp, empty log files are not rotated, old logs are removed
considering log /var/log/will-log
log needs rotating
rotating log /var/log/will-log, log->rotateCount is 7
dateext suffix '-20160401'
glob pattern '-[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]'
glob finding logs to compress failed
glob finding old rotated logs failed
renaming /var/log/will-log to /tmp/will-log-20160401
creating new /var/log/will-log mode = 0644 uid = 0 gid = 0
测试没有问题的话，可以在定时任务执行起，手动执行一次
# logrotate -f /etc/logrotate.d/will-log
实际情况下，还得通知应用服务重载配置，一般会在最后加上重启命令，以Nginx为例：
postrotate
[ -f /var/run/nginx.pid ] && kill -USR1 `cat /var/run/nginx.pid`
endscript
USR1亦通常被用来告知应用程序重载配置文件；例如，向Apache HTTP服务器发送一个USR1信号将导致以下步骤的发生：停止接受新的连接，等待当前连接停止，重新载入配置文件，重新打开日志文件，重启服务器，从而实现相对平滑的不关机的更改。
内容来自维基SIGUSR1和SIGUSR2
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