程式生成的日誌檔案一般需要定期清理，不然既浪費空間又不便於檢視。

linux中有個logrotate的程式可以很方便的配置日誌清理規則（可以根據時間，日誌檔案大小等來進行日誌的清理）。

介紹一下幾種配置模式…

create 模式：

重新命名原先的日誌檔案，並通知程式重新開啟一個日誌檔案（重啟程式，或者傳送訊號通知應用程式重新開啟一個日誌檔案）。

Logrotate size option: Rotate the log file when file size reaches a specific limit

If you want to rotate a log file (for
 
 example, /tmp/output.log) for every 1KB, create the logrotate.conf as shown below.

$ cat logrotate.conf
/tmp/output.log {
        size 1k
        create 700 bala bala
        rotate 4
}
This logrotate configuration has following three options:

size 1k – logrotate runs only if the filesize is equal to (or
 
 greater than) this size.
create – rotate the original file and create the new file with specified permission, user and group.
rotate – limits the number of log file rotation. So, this would keep only the recent 4 rotated log files.

copytruncate 模式：

複製日誌檔案中的內容到其他檔案中，並將該日誌檔案的size設定為0。
注意：如果檔案不是以APPEND

Logrotate copytruncate option: Continue to write the log information in the newly created file after rotating the old log file.

$ cat logrotate.conf
/tmp/output.log {
         size 1k
         copytruncate
         rotate 4
}
copytruncate instruct logrotate to creates the copy of the original file (i.e rotate the original log file) and truncates the original file to zero byte size. This helps the respective service that belongs to that log file can write to the proper file.

以APPEND模式開啟就是這樣的：

std::ofstream ofs;
ofs.open ("test.txt", std::ofstream::out | std::ofstream::app)

或者：

FILE* logfile
logfile = fopen("abc.log","wa");

這樣的缺點就是程式每一次啟動時，如果已經存在一個對應的檔案，最新的日誌就會追加到該檔案末尾，而不是清空該日誌檔案然後再寫入。

一個可用的配置如下：

# 配置需要rotate的檔案，和 size 等
[email protected]:~/robotwork$ cat /etc/logrotate.d/guowei.log
/home/guowei/robotwork/*.log {
        rotate 2
        size 30k
        copytruncate
        notifempty
        missingok
}

# 然後配置每個小時 rotate一下( cp /etc/cron.daily/logrotate /etc/cron.hourly/ )：
[email protected]:~/robotwork$ cat /etc/cron.hourly/logrotate 
#!/bin/sh

# Clean non existent log file entries from status file
cd /var/lib/logrotate
test -e status || touch status
head -1 status > status.clean
sed 's/"//g' status | while read logfile date
do
    [ -e "$logfile" ] && echo "\"$logfile\" $date"
done >> status.clean
mv status.clean status

test -x /usr/sbin/logrotate || exit 0
/usr/sbin/logrotate /etc/logrotate.conf

按照上述配置好後，然後執行一下這個，你就會發現你的日誌檔案被rotate了：

sudo run-parts /etc/cron.daily  # or cron.hourly