centos8使用df命令查看磁盘占用，数据刷新不及时

磁盘要用完了，在清理数据。清理过程中，用df查看磁盘占用情况。发现df的结果有延迟。大概几分钟，10分钟以内。

[root@10-100-0-18 ~]# df
Filesystem      1K-blocks       Used Available Use% Mounted on
devtmpfs          8073048          0   8073048   0% /dev
tmpfs             8089888        368   8089520   1% /dev/shm
tmpfs             8089888     860784   7229104  11% /run
tmpfs             8089888          0   8089888   0% /sys/fs/cgroup
/dev/vda3        36681220    9281392  27399828  26% /
/dev/sda1      1055840692  198940492 803196728  20% /data
/dev/sda2      1055839648 1006859920         0 100% /file
/dev/vda1          999320     245632    684876  27% /boot
tmpfs             1617976          0   1617976   0% /run/user/0
[root@10-100-0-18 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        7.7G     0  7.7G   0% /dev
tmpfs           7.8G  368K  7.8G   1% /dev/shm
tmpfs           7.8G  841M  6.9G  11% /run
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/vda3        35G  8.9G   27G  26% /
/dev/sda1      1007G  190G  766G  20% /data
/dev/sda2      1007G  961G     0 100% /file
/dev/vda1       976M  240M  669M  27% /boot
tmpfs           1.6G     0  1.6G   0% /run/user/0
[root@10-100-0-18 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        7.7G     0  7.7G   0% /dev
tmpfs           7.8G  368K  7.8G   1% /dev/shm
tmpfs           7.8G  841M  6.9G  11% /run
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/vda3        35G  8.9G   27G  26% /
/dev/sda1      1007G  190G  766G  20% /data
/dev/sda2      1007G  960G     0 100% /file
/dev/vda1       976M  240M  669M  27% /boot
tmpfs           1.6G     0  1.6G   0% /run/user/0
[root@10-100-0-18 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        7.7G     0  7.7G   0% /dev
tmpfs           7.8G  368K  7.8G   1% /dev/shm
tmpfs           7.8G  841M  6.9G  11% /run
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/vda3        35G  8.9G   27G  26% /
/dev/sda1      1007G  190G  766G  20% /data
/dev/sda2      1007G  960G     0 100% /file
/dev/vda1       976M  240M  669M  27% /boot
tmpfs           1.6G     0  1.6G   0% /run/user/0
[root@10-100-0-18 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        7.7G     0  7.7G   0% /dev
tmpfs           7.8G  368K  7.8G   1% /dev/shm
tmpfs           7.8G  841M  6.9G  11% /run
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/vda3        35G  8.9G   27G  26% /
/dev/sda1      1007G  190G  766G  20% /data
/dev/sda2      1007G  959G     0 100% /file
/dev/vda1       976M  240M  669M  27% /boot
tmpfs           1.6G     0  1.6G   0% /run/user/0
[root@10-100-0-18 ~]# cat /etc/redhat-release
CentOS Stream release 8

[root@10-100-0-18 ~]# df
Filesystem 1K-blocks Used Available Use% Mounted on
devtmpfs 8073048 0 8073048 0% /dev
tmpfs 8089888 368 8089520 1% /dev/shm
tmpfs 8089888 860784 7229104 11% /run
tmpfs 8089888 0 8089888 0% /sys/fs/cgroup
/dev/vda3 36681220 9281332 27399888 26% /
/dev/sda1 1055840692 198936468 803200752 20% /data
/dev/sda2 1055839648 1004764256 0 100% /file
/dev/vda1 999320 245632 684876 27% /boot
tmpfs 1617976 0 1617976 0% /run/user/0

过了几分钟之后：

[root@10-100-0-18 ~]# df
Filesystem      1K-blocks       Used Available Use% Mounted on
devtmpfs          8073048          0   8073048   0% /dev
tmpfs             8089888        368   8089520   1% /dev/shm
tmpfs             8089888     860784   7229104  11% /run
tmpfs             8089888          0   8089888   0% /sys/fs/cgroup
/dev/vda3        36681220    9281332  27399888  26% /
/dev/sda1      1055840692  198940832 803196388  20% /data
/dev/sda2      1055839648 1001511260    624968 100% /file
/dev/vda1          999320     245632    684876  27% /boot
tmpfs             1617976          0   1617976   0% /run/user/0