在清理大文件时，因为文件被占用时，无法通过rm直接删除并获取的对应的空间，为此需要通过cat /dev/null > bigfile的方式来获得。
[root@localhost /]# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda3 18555904 3951572 14604332 22% / devtmpfs 907532 0 907532 0% /dev tmpfs 922056 84 921972 1% /dev/shm tmpfs 922056 9188 912868 1% /run tmpfs 922056 0 922056 0% /sys/fs/cgroup /dev/sda1 303788 147160 156628 49% /boot tmpfs 184412 16 184396 1% /run/user/42 tmpfs 184412 0 184412 0% /run/user/0 [root@localhost /]# dd if=/dev/zero of=/boot/bigfile bs=1M count=200 dd: error writing ‘/boot/bigfile’: No space left on device 153+0 records in 152+0 records out 160362496 bytes (160 MB) copied, 1.49218 s, 107 MB/s [root@localhost /]# df -H Filesystem Size Used Avail Use% Mounted on /dev/sda3 20G 4.1G 15G 22% / devtmpfs 930M 0 930M 0% /dev tmpfs 945M 87k 945M 1% /dev/shm tmpfs 945M 9.5M 935M 1% /run tmpfs 945M 0 945M 0% /sys/fs/cgroup /dev/sda1 312M 312M 21k 100% /boot tmpfs 189M 17k 189M 1% /run/user/42 tmpfs 189M 0 189M 0% /run/user/0 [root@localhost /]# df -H Filesystem Size Used Avail Use% Mounted on /dev/sda3 20G 4.1G 15G 22% / devtmpfs 930M 0 930M 0% /dev tmpfs 945M 87k 945M 1% /dev/shm tmpfs 945M 9.5M 935M 2% /run tmpfs 945M 0 945M 0% /sys/fs/cgroup /dev/sda1 312M 312M 21k 100% /boot tmpfs 189M 17k 189M 1% /run/user/42 tmpfs 189M 0 189M 0% /run/user/0 [root@localhost /]# cd /dev/sda1 /dev/sda1: Not a directory. [root@localhost /]# cd /boot [root@localhost /boot]# ls bigfile config-3.10.0-327.el7.x86_64 grub grub2 initramfs-0-rescue-10036d8e70354dcba552a570eb465320.img initramfs-3.10.0-327.el7.x86_64.img initramfs-3.10.0-327.el7.x86_64kdump.img initrd-plymouth.img symvers-3.10.0-327.el7.x86_64.gz System.map-3.10.0-327.el7.x86_64 vmlinuz-0-rescue-10036d8e70354dcba552a570eb465320 vmlinuz-3.10.0-327.el7.x86_64 [root@localhost /boot]# rm -f bigfile [root@localhost /boot]# df -H Filesystem Size Used Avail Use% Mounted on /dev/sda3 20G 4.1G 15G 22% / devtmpfs 930M 0 930M 0% /dev tmpfs 945M 87k 945M 1% /dev/shm tmpfs 945M 9.5M 935M 2% /run tmpfs 945M 0 945M 0% /sys/fs/cgroup /dev/sda1 312M 312M 21k 100% /boot tmpfs 189M 17k 189M 1% /run/user/42 tmpfs 189M 0 189M 0% /run/user/0 [root@localhost /boot]# df -H Filesystem Size Used Avail Use% Mounted on /dev/sda3 20G 4.1G 15G 22% / devtmpfs 930M 0 930M 0% /dev tmpfs 945M 87k 945M 1% /dev/shm tmpfs 945M 9.5M 935M 2% /run tmpfs 945M 0 945M 0% /sys/fs/cgroup /dev/sda1 312M 312M 21k 100% /boot tmpfs 189M 17k 189M 1% /run/user/42 tmpfs 189M 0 189M 0% /run/user/0 [root@localhost /boot]# rm -f bigfile [root@localhost /boot]# df -H Filesystem Size Used Avail Use% Mounted on /dev/sda3 20G 4.1G 15G 22% / devtmpfs 930M 0 930M 0% /dev tmpfs 945M 87k 945M 1% /dev/shm tmpfs 945M 9.5M 935M 2% /run tmpfs 945M 0 945M 0% /sys/fs/cgroup /dev/sda1 312M 312M 21k 100% /boot tmpfs 189M 17k 189M 1% /run/user/42 tmpfs 189M 0 189M 0% /run/user/0 [root@localhost /boot]# cat /dev/null > bigfile [root@localhost /boot]# df -H Filesystem Size Used Avail Use% Mounted on /dev/sda3 20G 4.1G 15G 22% / devtmpfs 930M 0 930M 0% /dev tmpfs 945M 87k 945M 1% /dev/shm tmpfs 945M 9.5M 935M 2% /run tmpfs 945M 0 945M 0% /sys/fs/cgroup /dev/sda1 312M 151M 161M 49% /boot tmpfs 189M 17k 189M 1% /run/user/42 tmpfs 189M 0 189M 0% /run/user/0