System information

Sharing and maintaining SLES 10 SP2 Linux under z/VM 13
the program. The reasoning behind this is for compliance with IEEE standard P1003.2
(POSIX, part 2).”
In the read-only root system /tmp is actually an in-memory only virtual file system as well, for
more information see tmpfs (also known as SHMFS).
/usr
The LSB states that:
“/usr usually contains by far the largest share of data on a system. Hence, this is one of
the most important directories in the system as it contains all the user binaries, their
documentation, libraries, header files, etc.... X and its supporting libraries can be found
here. User programs like telnet, ftp, etc.... are also placed here. In the original Unix
implementations, /usr was where the home directories of the users were placed (that is to
say, /usr/someone was then the directory now known as /home/someone). In current
Unices, /usr is where user-land programs and data (as opposed to 'system land' programs
and data) are. The name hasn't changed, but it's meaning has narrowed and lengthened
from “everything user related” to “user usable programs and data”. As such, some people
may now refer to this directory as meaning 'User System Resources' and not 'user' as was
originally intended.”
The FHS states:
“/usr is shareable, read-only data. That means that /usr should be shareable between
various FHS-compliant hosts and must not be written to. Any information that is
host-specific or varies with time is stored elsewhere.
Large software packages must not use a direct subdirectory under the /usr hierarchy.”
/var
The LSB states that:
“(/var) Contains variable data like system logging files, mail and printer spool directories,
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'
contains variable data, i.e. files and directories the system must be able to write to during
operation.
The FHS states:
“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.”
/srv
The FHS states:
“/srv contains site-specific data which is served by this system. This main purpose of
specifying this is so that users may find the location of the data files for particular service,
and so that services which require a single tree for read-only data, writable data and
scripts (such as CGI scripts) can be reasonably placed. Data that is only of interest to a
specific user should go in that users' home directory.