头条刷搞笑段子的时候 偶然看到某厂面试里有这么一道题
大概意思是：
服务器磁盘空间占用很大（df 命令查看），但是去每个分区查找的话，占用磁盘空间缺很小（du 命令），请问为什么呢？
今天就通过实践跟大家讲下这个问题
1、登录服务器 查看磁盘空间占用比较多，200 多 G
$ df -lh
Filesystem Size Used Avail Use% Mounted on
dev/sda2 259G 210G 37G 86% /
tmpfs 32G 20K 32G 1% /dev/shm
/dev/sda1 240M 34M 194M 15% /boot
/dev/sdb1 1.1T 171M 1.1T 1% /data
2、去每个分区看磁盘总空间不多，du -sh
3、怀疑是某进程写的日志文件被删了，但是进程还一直存在
$ lsof |grep deleted
zabbix_ag 3586 zabbix 1w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3586 zabbix 2w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3593 zabbix 1w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3593 zabbix 2w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3594 zabbix 1w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3594 zabbix 2w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3595 zabbix 1w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3595 zabbix 2w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3596 zabbix 1w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3596 zabbix 2w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3598 zabbix 1w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
zabbix_ag 3598 zabbix 2w REG 8,2 926 3670771 /var/log/zabbix/zabbix_agentd.log-20200326 (deleted)
docker 3627 root txt REG 8,2 14243454 533156 /usr/bin/docker (deleted)
salt-mini 4097 root txt REG 8,2 9032 526442 /usr/bin/python2.6 (deleted)
salt-mini 4097 root 0r REG 8,2 17 5767173 /tmp/sh-thd-1585122196 (deleted)
salt-mini 4097 root 6w REG 8,2 3442 3801977 /var/log/salt/minion-20201020 (deleted)
salt-mini 4098 root txt REG 8,2 9032 526442 /usr/bin/python2.6 (deleted)
salt-mini 4098 root 0r REG 8,2 17 5767173 /tmp/sh-thd-1585122196 (deleted)
salt-mini 4098 root 6w REG 8,2 3442 3801977 /var/log/salt/minion-20201020 (deleted)
java 94075 root 1w REG 8,2 193473089391 2490385 /root/test1/dubbo-governance.log.100 (deleted)
java 94075 root 2w REG 8,2 193473089391 2490385 /root/test1/dubbo-governance.log.100 (deleted)
其中第 7 列里有个 193473089391 值比较大，这列代表文件大小，单位为 B
193473089391 /（1024 * 1024 *1 024 ）= 180 G
4、查进程
$ ps -ef|grep 94075
root 88886 87352 0 11:30 pts/0 00:00:00 grep 94075
root 94075 1 31 2020 ? 24-16:33:21 /usr/java/jdk1.8.0_131/bin/java -jar dubbo-admin-0.0.1-SNAPSHOT.jar
5、杀死进程
6、查看磁盘空间
$ df -lh
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 259G 30G 217G 12% /
tmpfs 32G 20K 32G 1% /dev/shm
/dev/sda1 240M 34M 194M 15% /boot
/dev/sdb1 1.1T 171M 1.1T 1% /data
磁盘空间使用了 30G，磁盘空间释放前使用 210G，释放了 180G，验证正确