Red Hat Bugzilla – Bug 98312
screen fail attempting to reopen tty
Last modified: 2007-04-18 12:55:23 EDT
Description of problem:
screen try to open the current tty, this is not always possible.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Log in as user1
2. Use su to switch to user2
3. start screen
An error message apears (terminal name may differ):
Cannot open your terminal '/dev/pts/3' - please check.
screen starts and works as if user2 had logged in
There is no problem in the case when using su to switch
to the root user. There is only a problem if user2 is
not root. screen should be able to work by using an
already open file descriptor or /dev/tty.
A user's terminal device is not readable/writeable by other users by default; to
do otherwise would pose quite a security problem. Root does not have this
limitation (because root can read/write anything). I DO NOT recommend this, but
if you *really* want another user to be able to open your tty (using 'su' is,
for all intensive purposes, the same as another user):
chmod 666 /dev/pts/2
The reason 'su' doesn't have this problem is because it doesn't open a new TTY.
It merely spawns a new shell and pipes input/output from the child session to
the parent TTY - which is why 'su' does not need to change the TTY's ownership
or permissions. (Again, changing TTY ownerships and permissions is generally
Applications, such as screen, which require direct access to the controlling
terminal must have read/write access as the _current_ UID.
Another way to do it would be to simply SSH in as the user you intend to run
screen as, or alternatively run screen and then run 'su' within the screen sessions.