收到空间报警，查看磁盘使用率：
df -h
文件系统 容量 已用 可用 已用% 挂载点
/dev/sda2 8.2G 7.4G 824M 91% /
tmpfs 32G 0 32G 0% /dev/shm
/dev/sda3 814G 281G 533G 35% /home
查看跟系统的容量大小才5G，莫名其妙的3G去哪里了
# /usr/sbin/lsof | grep deleted
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
dbus-daem 3798 dbus txt REG 8,2 306992 129307 /bin/dbus-daemon (deleted)
sendmail 12457 smmsp 3uW REG 8,2 2726449152 461233 /var/spool/clientmqueue/dft1PEU79a012457 (deleted)
salt-mini 13932 root 3w REG 8,2 1090 129441 /var/log/salt/minion.1 (deleted)
salt-mini 13932 root 6u REG 8,2 4096 1007868 /tmp/ffioygjjP (deleted)
java 15894 root 8w REG 8,2 194 186377 /usr/local/tomcat/logs/localhost.2015-02-11.log (deleted)
java 15894 root 9w REG 8,2 0 186379 /usr/local/tomcat/logs/manager.2015-02-11.log (deleted)
java 15894 root 10w REG 8,2 0 186380 /usr/local/tomcat/logs/host-manager.2015-02-11.log (deleted)
php 18282 root 1w REG 8,2 169519016 1007917 /tmp/37_agent_logs.txt (deleted)
mysqld 19046 mysql 5u REG 8,3 0 84754434 /home/mysqldata/tmp/ibOqmX4t (deleted)
mysqld 19046 mysql 6u REG 8,3 0 84754435 /home/mysqldata/tmp/iblK1saZ (deleted)
mysqld 19046 mysql 7u REG 8,3 0 84754436 /home/mysqldata/tmp/ibRnPYfu (deleted)
mysqld 19046 mysql 8u REG 8,3 0 84754437 /home/mysqldata/tmp/ibP28SYZ (deleted)
mysqld 19046 mysql 12u REG 8,3 0 84754438 /home/mysqldata/tmp/ib9LZpRv (deleted)
mysqld 19046 mysql 330u REG 8,3 344400 84754439 /home/mysqldata/tmp/MLFsRpHN (deleted)
mysqld 19046 mysql 341u REG 8,3 627873 95371267 /home/mysqldata/tmp/ML79IaOC (deleted)
mysqld 19046 mysql 342u REG 8,3 660513 95371268 /home/mysqldata/tmp/MLCHNsTV (deleted)
mysqld 19046 mysql 362u REG 8,3 505386 95371269 /home/mysqldata/tmp/ML5MlvRl (deleted)
mysqld 19046 mysql 363u REG 8,3 470919 95371270 /home/mysqldata/tmp/ML5woLxX (deleted)
mysqld 19046 mysql 366u REG 8,3 423467 95371271 /home/mysqldata/tmp/MLXhbeXo (deleted)
mysqld 19046 mysql 449u REG 8,3 338708 95371275 /home/mysqldata/tmp/MLQNH97E (deleted)
mysqld 19046 mysql 457u REG 8,3 307053 95371272 /home/mysqldata/tmp/MLxRXI4B (deleted)
mysqld 19046 mysql 474u REG 8,3 202805 84754440 /home/mysqldata/tmp/MLjcsyFm (deleted)
mysqld 19046 mysql 475u REG 8,3 195019 103235585 /home/mysqldata/tmp/MLJ6u7kZ (deleted)
zabbix_ag 20583 zabbix 1w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20583 zabbix 2w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20583 zabbix 3wW REG 8,2 5 1007929 /tmp/zabbix_agentd.pid (deleted)
zabbix_ag 20585 zabbix 1w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20585 zabbix 2w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20585 zabbix 3w REG 8,2 5 1007929 /tmp/zabbix_agentd.pid (deleted)
zabbix_ag 20586 zabbix 1w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20586 zabbix 2w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20586 zabbix 3w REG 8,2 5 1007929 /tmp/zabbix_agentd.pid (deleted)
zabbix_ag 20587 zabbix 1w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20587 zabbix 2w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20587 zabbix 3w REG 8,2 5 1007929 /tmp/zabbix_agentd.pid (deleted)
zabbix_ag 20588 zabbix 1w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20588 zabbix 2w REG 8,2 1048596 1007842 /tmp/zabbix_agentd.log.old (deleted)
zabbix_ag 20588 zabbix 3w REG 8,2 5 1007929 /tmp/zabbix_agentd.pid (deleted)
zabbix_ag 20589 zabbix 3w REG 8,2 5 1007929 /tmp/zabbix_agentd.pid (deleted)
末尾这个(deleted)说明此文件已经被删掉了，但是由于sendmail这个进程打开了这个文件，所以在硬盘上仍然存在着这个文件，但是却不能被文件系统识别，而df命令在计算used空间时，会将这部分文件包括在内。于是重启sendmail解决。