df refresh磁盘没同步 - 好文

<>文件清理后，磁盘没及时同步。

事件：发现 df 不足，检查是某个日志太大，于是删除日志，再次 df -h 检查磁盘。发现没及时同步。
root@远盛09-GPU号(70-85-C2-88-27-97):/# df -h 文件系统容量已用可用已用% 挂载点 udev 3.9G 0
3.9G 0% /dev tmpfs 790M 70M 720M 9% /run /dev/sda1 32G 20G 11G 64% / tmpfs 3.9G
252K 3.9G 1% /dev/shm tmpfs 5.0M 4.0K 5.0M 1% /run/lock tmpfs 3.9G 0 3.9G 0%
/sys/fs/cgroup /dev/sda2 174G 46G 120G 28% /data tmpfs 1000M 370M 631M 37%
/data/tmp tmpfs 790M 4.0K 790M 1% /run/user/112 tmpfs 790M 0 790M 0%
/run/user/1000 root@远盛09-GPU号(70-85-C2-88-27-97):/# du -sh
/var/log/obsolete-flaw-checker-log/* |grep G 5.7G
/var/log/obsolete-flaw-checker-log/flawChecker_2019-03-19.log
root@远盛09-GPU号(70-85-C2-88-27-97):/# rm -rf
/var/log/obsolete-flaw-checker-log/flawChecker_2019-03-19.log
root@远盛09-GPU号(70-85-C2-88-27-97):/# du -sh
/var/log/obsolete-flaw-checker-log/* |grep M 657M
/var/log/obsolete-flaw-checker-log/flawChecker_2019-03-19.log00000
root@远盛09-GPU号(70-85-C2-88-27-97):/# rm -rf
/var/log/obsolete-flaw-checker-log/flawChecker_2019-03-19.log00000
root@远盛09-GPU号(70-85-C2-88-27-97):/# df -h 文件系统容量已用可用已用% 挂载点 udev 3.9G 0
3.9G 0% /dev tmpfs 790M 70M 720M 9% /run /dev/sda1 32G 19G 12G 62% / tmpfs 3.9G
252K 3.9G 1% /dev/shm tmpfs 5.0M 4.0K 5.0M 1% /run/lock tmpfs 3.9G 0 3.9G 0%
/sys/fs/cgroup /dev/sda2 174G 46G 120G 28% /data tmpfs 1000M 370M 631M 37%
/data/tmp tmpfs 790M 4.0K 790M 1% /run/user/112 tmpfs 790M 0 790M 0%
/run/user/1000
<>文件（你删除的）仍被进程占用，所以空间没释放

使用这个命令就可以查看。
# lsof | grep 'deleted' # ls -ld /proc/* | grep '(deleted)'
参考链接(
https://ma.ttias.be/df-command-in-linux-not-updating-actual-diskspace-wrong-data/

<https://ma.ttias.be/df-command-in-linux-not-updating-actual-diskspace-wrong-data/>
)
以下是原文，
Caused by open file descriptors

If you delete files from the filesystem, the command “df -h” might not show
the deleted space as being available. This is because the deleted files could
still be held open by (defunct) processes, where the file descriptor handles
still point to those files. As a result, the df command assumes the files are
still there, and doesn’t clear the space.

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