Wandering Thoughts: Recent Entries For 2006/01/31

Getting console messages in X

As a system administrator, I like to see console messages even when I'm in X (which is almost all of the time). On my systems, console messages come from high priority kernel messages, high priority notes from syslog, and sometimes messages from init, and I like to know about all of these.

In theory, xterm's -C command line switch should do this nicely, and indeed it did for years. These days, there are two unfortunate problems with it:

• back in 2001 or so, the xterm people decided that -C should quietly ignore your request if you didn't own /dev/console.
• around about the 2.6.9 or 2.6.10 kernel, the Linux kernel people decided that you couldn't redirect console messages unless you were root.

I strongly disagree with xterm's paranoia, since it's pointless if xterm is unprivileged (which it almost always is, and the code could always just check). If xterm has no special privileges, the user can just write their own program to do the appropriate TIOCCONS operation; all blocking -C from working does is inconvenience people.

So back in 2001 I grumbled and wrote my own ten line program to do the needed TIOCCONS ioctl, and there things sat until recently.

Getting around the 'only root can use TIOCCONS' problem is a little bit more work. Since I'm the only user of my machine, I just made my getconsole program from 2001 setuid root and group-executable only by me. A more general solution would be a program that checks the ownership or permissions of /dev/console and only does the TIOCCONS if the person running it has appropriate access.

It's possible that xconsole in recent distributions already does this, but I personally suspect not. Certainly the Fedora Core 4 version shows no likely signs of this.