Chapter 28. Console Access
When normal (non-root) users log into a computer locally, they are
given two types of special permissions:
They can run certain programs that they would not otherwise be able
to run
They can access certain files (normally special device files used to
access diskettes, CD-ROMs, and so on) that they would not otherwise
be able to access
Since there are multiple consoles on a single computer and multiple users
can be logged into the computer locally at the same time, one of the users
has to essentially win the race to access the files. The first user to log
in at the console owns those files. Once the first user logs out, the
next user who logs in owns the files.
In contrast, every user who logs in at the console is
allowed to run programs that accomplish tasks normally restricted to the
root user. If X is running, these actions can be included as menu items
in a graphical user interface. As shipped, the console-accessible
programs include halt, poweroff, and
reboot.
By default, /etc/inittab specifies that your system
is set to shutdown and reboot in response to a [Ctrl]-[Alt]-[Del] key combination used at the console. To completely disable
this ability, comment out the following line in
/etc/inittab by putting a hash mark
(#) in front of it:
ca::ctrlaltdel:/sbin/shutdown -t3 -r now |
Alternatively, you may want to allow certain non-root users the
right to shutdown or reboot the system from the console using [Ctrl]-[Alt]-[Del]. You can restrict this privilege to certain users, by
taking the following steps:
Add the -a option to the
/etc/inittab line shown above, so that it
reads:
ca::ctrlaltdel:/sbin/shutdown -a -t3 -r now |
The -a flag tells shutdown
to look for the /etc/shutdown.allow file.
Create a file named shutdown.allow in
/etc. The
shutdown.allow file should list the usernames
of any users who are allowed to shutdown the system using
[Ctrl]-[Alt]-[Del]. The format of the
shutdown.allow file is a list of
usernames, one per line, like the following:
According to this example shutdown.allow file, the
users stephen, jack, and sophie are allowed to shutdown the system from
the console using [Ctrl]-[Alt]-[Del]. When that key combination is used,
the shutdown -a command in
/etc/inittab checks to see if any of the users in
/etc/shutdown.allow (or root) are logged in on a
virtual console. If one of them is, the shutdown of the system
continues; if not, an error message is written to the system console
instead.
For more information on shutdown.allow, refer to the
shutdown man page.
