- /etc/rc or
/etc/rc.d or
/etc/rc?.d
Scripts or directories of scripts
to run at startup or when changing the run level.
See Chapter 9 for further
information.
- /etc/passwd
The user database, with fields giving the
username, real name, home directory, encrypted password, and
other information about each user. The format is documented
in the passwd manual page. The encrypted
passwords are much more commonly found in the
/etc/shadow these days. This means
that almost everything about the user
except the password is stored in the
passwd file. History and convention
make a name change undesirable.
- /etc/fdprm
Floppy disk parameter table.
Describes what different floppy disk formats look
like. Used by setfdprm. See the
setfdprm manual page for more
information.
- /etc/fstab
Lists the filesystems mounted automatically
at startup by the mount -a command (in
/etc/rc or equivalent startup file).
Under Linux, also contains information about swap areas used
automatically by swapon -a. See the Section called Mounting and unmounting in Chapter 6 and the mount
manual page for more information. Also
fstab usually has its own manual page in
section 5.
- /etc/group
Similar to /etc/passwd,
but describes groups instead of users. See the
group manual page in section 5 for more
information.
- /etc/inittab
Configuration file for
init.
- /etc/issue
Output by getty before
the login prompt. Usually contains a short description or
welcoming message to the system. The contents are up to
the system administrator.
- /etc/magic
The configuration file
for file. Contains the
descriptions of various file formats based on
which file guesses the type of
the file. See the magic and
file manual pages for more information.
- /etc/motd
The message of the day, automatically
output after a successful login. Contents are up to the
system administrator. Often used for getting information
to every user, such as warnings about planned downtimes.
- /etc/mtab
List of currently mounted filesystems.
Initially set up by the bootup scripts, and updated
automatically by the mount
command. Used when a list of mounted filesystems is
needed, e.g., by the df command.
- /etc/shadow
Shadow password file on systems with shadow
password software installed. Shadow passwords move the
encrypted password from /etc/passwd
into /etc/shadow; the latter is not
readable by anyone except root. This makes it harder to
crack passwords. If your distribution gives you a choice
(many do) of whether or not to use shadow passwords then you
are highly recommended to do
so.
- /etc/login.defs
Configuration file for the
login command. The
login.defs file usually has a manual
page in section 5.
- /etc/printcap
Like /etc/termcap, but
intended for printers. However it uses different syntax.
The printcap has a manual page in
section 5.
- /etc/profile,
/etc/csh.login,
/etc/csh.cshrc
Files executed at login or startup time
by the Bourne or C shells. These allow the system
administrator to set global defaults for all users.
See the manual pages for the respective shells.
- /etc/securetty
Identifies secure terminals, i.e., the
terminals from which root is allowed to log in. Typically
only the virtual consoles are listed, so that it becomes
impossible (or at least harder) to gain superuser privileges
by breaking into a system over a modem or a network. Do not
allow root logins over a network. Prefer to log in as an
unprivileged user and use su or
sudo to gain root
privileges.
- /etc/shells
Lists trusted shells. The
chsh command allows users to change
their login shell only to shells listed in this file.
ftpd, the server process that provides
FTP services for a machine, will check that the user's
shell is listed in /etc/shells
and will not let people log in unless the shell is
listed there.
- /etc/termcap
The terminal capability database.
Describes by what ``escape sequences'' various terminals
can be controlled. Programs are written so that instead
of directly outputting an escape sequence that only
works on a particular brand of terminal, they look up
the correct sequence to do whatever it is they want to
do in /etc/termcap. As a result
most programs work with most kinds of terminals.
See the termcap, curs_termcap,
and terminfo manual pages for
more information.