私のルートディレクトリがほとんどスペースを占めていませんが、ディスクスペースを占有しないのはなぜですか?

私のルートディレクトリがほとんどスペースを占めていませんが、ディスクスペースを占有しないのはなぜですか?

Ubuntu Linux 16を使用しています。ディスク容量が足りません。

[rails@server ~]$ df -h /
Filesystem      Size  Used Avail Use% Mounted on
/dev/simfs       30G   29G  1.5G  96% /

しかし、私が理解していないのは、「/」ディレクトリのフルサイズを取得すると29G未満で表示されることです。

[rails@server ~]$ sudo du -sh /
du: cannot access ‘/proc/883/task/883/fd/4’: No such file or directory
du: cannot access ‘/proc/883/task/883/fdinfo/4’: No such file or directory
du: cannot access ‘/proc/883/fd/4’: No such file or directory
du: cannot access ‘/proc/883/fdinfo/4’: No such file or directory
4.5G    /

ここで何が起こっているのでしょうか?さらに重要なのは、この不思議なディスクスペースがすべてどこで使用されているのか、どうすればわかりますか?

編集する:

GracefulRestartの要件に従って出力されます...

[rails@server ~]$ sudo lsof -nP 2>&1 | grep 'deleted'
postmaste  443      postgres  mem       REG              144,4           147159237 (deleted)/dev/zero (stat: No such file or directory)
postmaste  443      postgres  mem       REG              144,4                   0 (deleted)/VE20428-SYSV0052e2c1 (stat: No such file or directory)
postmaste  469      postgres  mem       REG              144,4           147159237 (deleted)/dev/zero (stat: No such file or directory)
postmaste  469      postgres  mem       REG              144,4                   0 (deleted)/VE20428-SYSV0052e2c1 (stat: No such file or directory)
postmaste  470      postgres  mem       REG              144,4           147159237 (deleted)/dev/zero (stat: No such file or directory)
postmaste  470      postgres  mem       REG              144,4                   0 (deleted)/VE20428-SYSV0052e2c1 (stat: No such file or directory)
postmaste  471      postgres  mem       REG              144,4           147159237 (deleted)/dev/zero (stat: No such file or directory)
postmaste  471      postgres  mem       REG              144,4                   0 (deleted)/VE20428-SYSV0052e2c1 (stat: No such file or directory)
postmaste  472      postgres  mem       REG              144,4           147159237 (deleted)/dev/zero (stat: No such file or directory)
postmaste  472      postgres  mem       REG              144,4                   0 (deleted)/VE20428-SYSV0052e2c1 (stat: No such file or directory)
httpd     1130          root  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1130          root  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131        apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131        apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1133   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1133   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1134   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1134   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1135   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1135   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1136   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1136   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1137   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1137   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1138   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1138   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1139   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1139   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1140   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1140   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1141   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1141   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1142   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1142   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1143   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1143   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1144   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1144   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1145   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1145   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1146   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1146   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1147   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1147   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1148   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1148   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1131 1149   apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1131 1149   apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1132        apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1132        apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
httpd     1158        apache  mem       REG              144,4           147485837 (deleted)/dev/zero (stat: No such file or directory)
httpd     1158        apache  mem       REG              144,4               65537 (deleted)/VE20428-SYSV0176748a (stat: No such file or directory)
postmaste 1270      postgres  mem       REG              144,4           147159237 (deleted)/dev/zero (stat: No such file or directory)
postmaste 1270      postgres  mem       REG              144,4                   0 (deleted)/VE20428-SYSV0052e2c1 (stat: No such file or directory)

編集2:2番目のコマンドの結果は次のとおりです。

[rails@server ~]$ sudo du -h --max-depth=1 /; ls -plah / | grep -v /
214M    /opt
4.0K    /media
12K /boot
6.7M    /run
4.0K    /lost+found
du: cannot access ‘/proc/3478/task/3478/fd/4’: No such file or directory
du: cannot access ‘/proc/3478/task/3478/fdinfo/4’: No such file or directory
du: cannot access ‘/proc/3478/fd/4’: No such file or directory
du: cannot access ‘/proc/3478/fdinfo/4’: No such file or directory
0   /proc
4.0K    /dev
4.0K    /.cpt_hardlink_dir_a920e4ddc233afddc9fb53d26c392319
114M    /tmp
0   /sys
14M /etc
3.6M    /root
396M    /home
12K /.rbenv
4.0K    /srv
1.9G    /usr
1.9G    /var
8.0K    /mnt
4.5G    /
total 64K
-rw-r--r--  1 root root    0 May  5  2018 .autorelabel
-rw-r--r--  1 root root    0 Nov  8 17:14 reboot
-rw-r--r--  1 root root    0 Nov  8 17:15 .vzfifo

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