Why is space not being freed from disk after deleting a file in Red Hat Enterprise Linux?

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本文介绍在Red Hat Enterprise Linux中，当删除文件后，由于进程仍持有文件打开状态，导致磁盘空间未被释放的问题。提供了解决方案，包括优雅关闭相关进程和通过proc文件系统强制截断文件大小。

SOLUTION 已验证 - 已更新 2019年三月19日01:05 -

Why is space not being freed from disk after deleting a file in Red Hat Enterprise Linux?
When deleting a large file or files, the file is deleted successfully but the size of the filesystem does not reflect the change.
I've deleted some files but the amount of free space on the filesystem has not changed.
The OS was holding several very large log files open with some as large as ~30G. The file was previously deleted, but only stopping and restarting the jvm/java process released the disk space. The lsof command shows the following output before restarting the java process

Raw
```
COMMAND     PID      USER   FD      TYPE    DEVICE   SIZE/OFF       NODE NAME
: 
java      49097    awdmw   77w      REG     253,6 33955068440    1283397 /opt/jboss/jboss-eap-5/jboss-as/server/all/log/server.log (deleted)
```
When you perform a df, the storage shows 90+% utilized, however, there is not really that much written to that space.

Graceful shutdown of relevant process

First obtain a list of deleted files which are still held open by applications

$ /usr/sbin/lsof | grep deleted
ora    25575 data   33u   REG      65,65  4294983680   31014933 /oradata/DATAPRE/file.dbf (deleted)

From lsof output, we find the process with pid 25575 has kept file /oradata/DATAPRE/file.dbf open with file descriptor (fd) number 33
After a file has been identified you can free space occupied by this file by shutting down the process in question. If a graceful shutdown does not work, then you may issue the kill command to forcefully stop it by referencing the PID.

Truncate File Size

For example, from the lsof output above

$ file /proc/25575/fd/33
/proc/25575/fd/33: broken symbolic link to `/oradata/DATAPRE/file.dbf (deleted)'
$ echo > /proc/25575/fd/33

NOTE:

The same reason will cause different disk usage from du command and df command, please refer to Why does df show bigger disk usage than du?
If you want to know the size (in blocks) these files are occupying you can use a command like:

# lsof -Fn -Fs |grep -B1 -i deleted | grep ^s  | cut -c 2- | awk '{s+=$1} END {print s}'

On Linux or Unix systems, deleting a file via rm or through a file manager application will unlink the file from the file system's directory structure; however, if the file is still open (in use by a running process) it will still be accessible to this process and will continue to occupy space on disk. Therefore such processes may need to be restarted before that file's space will be cleared up on the filesystem.