On Fri, Jun 29, 2012 at 09:00:31AM +0100, Toby Speight wrote: > If I use plain 'chroot' to access a working system, with > SHELL=/bin/bash, I can type 'suspend' into bash, and get back to my > parent shell. > > If I use 'schroot' to do the same, then 'suspend' just hangs until I > go to another terminal and 'kill -CONT' the bash process. > > I would like schroot to behave the same as plain chroot. I appreciate > it might not be trivial (chroot doesn't have to do anything special, as > it simply exec()s the required command, whereas schroot would have to > detect its child stopping and do the same to itself - I've no idea how > to do that).
This is quite an interesting problem, and will need a bit more investigation before I find a solution. bash sets up its own process group on startup. When you call "suspend", it signals the whole process group to stop. But since schroot isn't in the same group, it's not suspended. Ideally, you would only run a login shell with schroot, but we're not in an ideal world ;) schroot uses PAM, and basically treats commands being run in the chroot as though they were run as a separate login, e.g. equivalent to running ssh or sudo. That said, it should be possible to do this. schroot itself isn't doing anything special by starting any new sessions with setsid or setpgid, and itself works perfectly well with job control. Try running any command other than a shell (e.g. "more" or anything you like, or run schroot as part of a pipeline e.g. "schroot ls -l / | less") and you'll see that it all works fine in that you can press C-Z and it all suspends properly. So to support suspending a shell within ourselves, I'm not sure what is best to do here. I'll try trapping SIGCONT/SIGSTOP, and then raise the same signal on ourselves. However, this could open a horrible can of worms, e.g. if you send SIGCONT to bash while schroot is stopped. We won't be restarted ourselves then, and bash might then immediately get SIGTTOU/IN etc. I also don't want to break schroot running correctly in the normal/pipeline cases shown above. Regards, Roger -- .''`. Roger Leigh : :' : Debian GNU/Linux http://people.debian.org/~rleigh/ `. `' Printing on GNU/Linux? http://gutenprint.sourceforge.net/ `- GPG Public Key: 0x25BFB848 Please GPG sign your mail. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
