Home » Questions » Computers [ Ask a new question ]

why does chvt work fine as a regular user on a virtual terminal, but not under X?

why does chvt work fine as a regular user on a virtual terminal, but not under X?

When I'm logged in as user "paul" on a virtual terminal (/dev/tty2 for example) and I type in "chvt 4" I get switched over to the virtual terminal for /dev/tty4 just fine.

Asked by: Guest | Views: 111
Total answers/comments: 1
Guest [Entry]

"From a security point-of-view, recall that X is designed to be used over the network as well as at the physical console. Virtual terminals aren't, so a login at the physical VT is a different security beast from X.

From this Debian bug report on the same error in fgconsole. Here's the breakdown of why chvt and friends can't access it from X:

It doesn’t only affect fgconsole, but
also chvt, openvt and any other kbd
utility which tries to get a console
file descriptor. These programs do
their job by trying to open/ioctl
these files (in this order):

/proc/self/fd/0 (is a pseudo tty in your case)
/dev/tty (also PTY)
/dev/tty0 (only accessible to root)
/dev/vc/0 (doesn’t exist nowadays)
/dev/console (root)
std{in,out,err} (PTY)

As none of these is able to respond to
a VT_GETSTATE ioctl, fgconsole and
friends fail.

The preferred solution to the issue is to use sudo. There are other options but they are less preferable in the general case due to security issues -- you may decide your situation can tolerate one or the other (emphasis mine):

So there is no real solution, if I don't use sudo?

You cannot change the permissions of /dev/tty0 or /dev/console without
opening a giant security hole. Setting the desired programs suid is an
option, but I’d stay away from it. sudo is much safer and can be
controlled in more detail."