/srv ：主要用来存储本机或本服务器提供的服务或数据。（用户主动生产的数据、对外提供服务）
/srv contains site-specific data which is served by this system.
/var ：系统产生的不可自动销毁的缓存文件、日志记录。（系统和程序运行后产生的数据、不对外提供服务、只能用户手动清理）（包括mail、数据库文件、日志文件）
/var contains variable data files. This
includes spool directories and files, administrative and logging data, and transient
and temporary files.
Some portions of /var are not shareable between different systems. For
instance, /var/log, /var/lock, and /var/run. Other
portions may be shared, notably /var/mail, /var/cache/man, /var/cache/fonts, and /var/spool/news.
/var is specified here in order to make it possible to mount /usr
read-only. Everything that once went into /usr that
is written to during system operation (as opposed to installation and software maintenance) must be in /var.
If /var cannot be made a separate partition, it is often preferable
to move /var out of the root partition and into the /usr
partition. (This is sometimes done to reduce the size of
the root partition or when space runs low in the root partition.) However,
/var must not be linked to /usr because this makes separation of /usr and /var more
difficult and is likely to create a naming conflict. Instead,
link /var to /usr/var.
Applications must generally not add directories to the top level
of /var. Such directories should only be added if they
have some system-wide implication, and in consultation with the FHS mailing list.
/tmp ：保存在使用完毕后可随时销毁的缓存文件。（有可能是由系统或程序产生、也有可能是用户主动放入的临时数据、系统会自动清理）
The /tmp directory must be made available for programs that require
temporary files.
Programs must not assume that any files or directories in /tmp are
preserved between invocations of the program.
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所以，服务器被用作Web开发时，html文件更应该被放在/srv/www下，而不是/var/www下（因为/srv目录是新标准中才有的，出现较晚；而且Apache将/var/www设为了web默认目录，所以现在绝大多数人都把web文件放在/var/www，这是个历史遗留问题）。
如ftp、流媒体服务等也应该被放在/srv对应的目录下。如果对应目录太大，应该另外挂载分区。