Linux + /tmp 下的文件和文件夾清理

在我所有的 Red Hat Linux 機器版本 7.2 上，我們看到 systemd-tmpfiles-clean.service 處於非活動狀態：

systemctl status systemd-tmpfiles-clean.service
● systemd-tmpfiles-clean.service - Cleanup of Temporary Directories
  Loaded: loaded (/usr/lib/systemd/system/systemd-tmpfiles-clean.service; static; vendor preset: disabled)
  Active: inactive (dead) since Wed 2018-12-19 14:47:14 UTC; 12min ago
    Docs: man:tmpfiles.d(5)
          man:systemd-tmpfiles(8)
 Process: 34231 ExecStart=/usr/bin/systemd-tmpfiles --clean (code=exited, status=0/SUCCESS)
Main PID: 34231 (code=exited, status=0/SUCCESS)

Dec 19 14:47:14 master02.uridns.com systemd[1]: Starting Cleanup of Temporary Directories...
Dec 19 14:47:14 master02.uridns.com systemd[1]: Started Cleanup of Temporary Directories.

奇怪的是，我們看到了 下的文件和文件夾/tmp，而且似乎每隔一段時間就會執行一次清理。

我在 crontab 或 cronjob 上進行了搜尋，但沒有找到其他清理工作。

我在這裡錯過了什麼嗎？

是否有可能儘管服務處於非活動狀態，但每隔幾週就會執行一次清理？

 systemctl enable  systemd-tmpfiles-clean.service

The unit files have no [Install] section. They are not meant to be enabled
using systemctl.
Possible reasons for having this kind of units are:
1) A unit may be statically enabled by being symlinked from another unit's
  .wants/ or .requires/ directory.
2) A unit's purpose may be to act as a helper for some other unit which has
  a requirement dependency on it.
3) A unit may be started when needed via activation (socket, path, timer,
  D-Bus, udev, scripted systemctl call, ...).

我們還看到了一些非常舊的文件夾，如

ls -ltr
total 137452
drwxr-xr-x 3 root      root         33 Jun 13  2017 Tools
drwx--x--x 3 root      root         16 Oct 12 09:33 systemd-private-74982d8a24254a1d8b8ec3b5c0d80a9b-httpd.service-QZqGLA
drwx--x--x 3 root      root         16 Oct 12 10:02 systemd-private-74982d8a24254a1d8b8ec3b5c0d80a9b-rtkit-daemon.service-BTcGY1
drwx--x--x 3 root      root         16 Oct 12 10:02 systemd-private-74982d8a24254a1d8b8ec3b5c0d80a9b-vmtoolsd.service-mQ1SXc
drwxr-xr-x 2 ambari    ambari       18 Oct 12 12:02 hsperfdata_ambari
drwx--x--x 3 root      root         16 Oct 12 12:17 systemd-private-74982d8a24254a1d8b8ec3b5c0d80a9b-cups.service-PnKaq8
drwx--x--x 3 root      root         16 Oct 12 12:17 systemd-private-74982d8a24254a1d8b8ec3b5c0d80a9b-colord.service-DNn470
-rwxr-xr-x 1 root      root      83044 Nov 18 17:27 Spark_Thrift.log
drwxr-xr-x 2 zookeeper hadoop       18 Nov 18 17:28 hsperfdata_zookeeper
-rwxr-xr-x 1 root      root        379 Nov 18 17:37 requests.txt
-rwxr-xr-x 1 root      root     137348 Nov 22 14:50 pp
-rwxr-xr-x 1 root      root        344 Nov 26 15:24 yy
prwx--x--x 1 root      root          0 Nov 29 21:26 hogsuspend
-rwxr-xr-x 1 root      root       1032 Dec  3 10:55 aa

從我的機器：

more /lib/systemd/system/systemd-tmpfiles-clean.timer
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Daily Cleanup of Temporary Directories
Documentation=man:tmpfiles.d(5) man:systemd-tmpfiles(8)

[Timer]
OnBootSec=15min
OnUnitActiveSec=1d

規則是：

more /usr/lib/tmpfiles.d/tmp.conf
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

# See tmpfiles.d(5) for details

# Clear tmp directories separately, to make them easier to override
v /tmp 1777 root root 10d
v /var/tmp 1777 root root 30d

# Exclude namespace mountpoints created with PrivateTmp=yes
x /tmp/systemd-private-%b-*
X /tmp/systemd-private-%b-*/tmp
x /var/tmp/systemd-private-%b-*
X /var/tmp/systemd-private-%b-*/tmp

你可以問 systemd 一個單元的觸發器是什麼：

systemctl show -p TriggeredBy systemd-tmpfiles-clean

這將表明該服務是由計時器systemd-tmpfiles-clean觸發的。systemd-tmpfiles-clean.timer這被定義為

#  SPDX-License-Identifier: LGPL-2.1+
#
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=Daily Cleanup of Temporary Directories
Documentation=man:tmpfiles.d(5) man:systemd-tmpfiles(8)

[Timer]
OnBootSec=15min
OnUnitActiveSec=1d

因此，該服務每天執行，並根據tmpfiles.d配置清理目錄。有關詳細資訊，請參閱相關的手冊頁。

引用自：https://unix.stackexchange.com/questions/489940