System information

12 Sharing and maintaining SLES 10 SP2 Linux under z/VM
“Although most distributions neglect to create the directories /opt/bin, /opt/doc,
/opt/include, /opt/info, /opt/lib, and /opt/man they are reserved for local system
administrator use. Packages may provide “front-end” files intended to be placed in (by
linking or copying) these reserved directories by the system administrator, but must
function normally in the absence of these reserved directories. Programs to be invoked by
users are located in the directory /opt/'package'/bin. If the package includes UNIX®
manual pages, they are located in /opt/'package'/man and the same substructure as
/usr/share/man must be used. Package files that are variable must be installed in /var/opt.
Host-specific configuration files are installed in /etc/opt.”
In the read-only root system at Nationwide, DB2® is installed under /opt/IBM/db2, MQ Series
is installed under /opt/mqm, with links into /usr/bin/ and /usr/lib/. So these mount points
are created early, while /opt/ is still read/write.
/proc
The LSB states that:
“/proc is very special in that it is also a virtual file system. It's sometimes referred to as a
process information pseudo-file system. It doesn't contain 'real' files but runtime system
information (e.g. system memory, devices mounted, hardware configuration, etc). For this
reason it can be regarded as a control and information center for the kernel. In fact, quite a
lot of system utilities are simply calls to files in this directory.”
/root
The LSB states that:
“This is the home directory of the System Administrator, 'root'. This may be somewhat
confusing ('root on root') but in former days, '/' was root's home directory (hence the name
of the Administrator account). To keep things tidier, 'root' got his own home directory. Why
not in '/home'? Because '/home' is often located on a different partition or even on another
system and would thus be inaccessible to 'root' when - for some reason - only '/' is
mounted.”
The FHS states that:
“If the home directory of the root account is not stored on the root partition it will be
necessary to make certain it will default to / if it can not be located.
We recommend against using the root account for tasks that can be performed as an
unprivileged user, and that it be used solely for system administration. For this reason, we
recommend that subdirectories for mail and other applications not appear in the root
account's home directory, and that mail for administration roles such as root, postmaster,
and web master be forwarded to an appropriate user.”
/tmp
The LSB states that:
“This directory contains mostly files that are required temporarily. Many programs use this
to create lock files and for temporary storage of data. Do not remove files from this
directory unless you know exactly what you are doing! Many of these files are important
for currently running programs and deleting them may result in a system crash. Usually it
won't contain more than a few KB anyway. On most systems, this directory is cleared out
at boot or at shutdown by the local system. The basis for this was historical precedent and
common practice. However, it was not made a requirement because system
administration is not within the scope of the FHS. For this reason people and programs
must not assume that any files or directories in /tmp are preserved between invocations of