我阅读了 William Shotts的 The Linux Command Line，其中有一些 Linux 文件（系统目录）的描述：
目录内容
/var不会改变。这棵树是存储可能更改的数据的地方。各种数据库、假脱机文件、用户邮件等都位于此处。
我想知道：如果/var目录内容不应该改变，为什么安装后会有一个www目录？/var/wwwapache-php
该/var/www目录是我们必须编辑、创建或删除文件的地方。这是一个本地主机公共目录。
为什么他说/var目录内容不会改变？
这种描述/var是自相矛盾的。/var包含易于更改的内容，例如网站、临时文件 ( /var/tmp) 和数据库。该名称是“变量”的缩写。
男子汉
/var This directory contains files which may change in size, such as spool and log files.
/var/account
Process accounting logs (optional).
/var/adm
This directory is superseded by /var/log and should be a symbolic link to /var/log.
/var/backups
Reserved for historical reasons.
/var/cache
Data cached for programs.
/var/cache/fonts
Locally-generated fonts (optional).
/var/cache/man
Locally-formatted man pages (optional).
/var/cache/www
WWW proxy or cache data (optional).
/var/cache/<package>
Package specific cache data (optional).
/var/catman/cat[1-9] or /var/cache/man/cat[1-9]
These directories contain preformatted manual pages according to their man page section. (The use of preformatted manual pages is deprecated.)
/var/crash
System crash dumps (optional).
/var/cron
Reserved for historical reasons.
/var/games
Variable game data (optional).
/var/lib
Variable state information for programs.
/var/lib/hwclock
State directory for hwclock (optional).
/var/lib/misc
Miscellaneous state data.
/var/lib/xdm
X display manager variable data (optional).
/var/lib/<editor>
Editor backup files and state (optional).
/var/lib/<name>
These directories must be used for all distribution packaging support.
/var/lib/<package>
State data for packages and subsystems (optional).
/var/lib/<pkgtool>
Packaging support files (optional).
/var/local
Variable data for /usr/local.
/var/lock
Lock files are placed in this directory. The naming convention for device lock files is LCK..<device> where <device> is the device's name in the filesystem. The format used is that of HDU
UUCP lock files, that is, lock files contain a PID as a 10-byte ASCII decimal number, followed by a newline character.
/var/log
Miscellaneous log files.
/var/opt
Variable data for /opt.
/var/mail
Users' mailboxes. Replaces /var/spool/mail.
/var/msgs
Reserved for historical reasons.
/var/preserve
Reserved for historical reasons.
/var/run
Run-time variable files, like files holding process identifiers (PIDs) and logged user information (utmp). Files in this directory are usually cleared when the system boots.
/var/spool
Spooled (or queued) files for various programs.
/var/spool
Spooled (or queued) files for various programs.
/var/spool/at
Spooled jobs for at(1).
/var/spool/cron
Spooled jobs for cron(8).
/var/spool/lpd
Spooled files for printing (optional).
/var/spool/lpd/printer
Spools for a specific printer (optional).
/var/spool/mail
Replaced by /var/mail.
/var/spool/mqueue
Queued outgoing mail (optional).
/var/spool/news
Spool directory for news (optional).
/var/spool/rwho
Spooled files for rwhod(8) (optional).
/var/spool/smail
Spooled files for the smail(1) mail delivery program.
/var/spool/uucp
Spooled files for uucp(1) (optional).
/var/tmp
Like /tmp, this directory holds temporary files stored for an unspecified duration.
/var/yp
Database files for NIS, formerly known as the Sun Yellow Pages (YP).
Linux File-system Hierarchy Standard和Linux Standard Base给出了预期可用的各种文件（包括目录）的定义。/ var 层次结构
包含可变数据文件。这包括假脱机目录和文件、管理和日志数据以及临时和临时文件。
有趣/var/www/的是没有在这样的规范规范中定义。
我会说 /var 中的内容不会经常更改。根据我的经验，它主要用于存储数据库文件、缓存文件，当然还有 /var/www 目录。这些对象确实会发生变化，但例如，网站不会每秒都在变化。