I have a minimal Linux system.
init is /bin/bash
, only bare minimum of libraries in /lib/
, /dev/
is populated statically, no daemons running (no udev, ..)
When bash starts, I get following error:
bash: cannot set terminal process group (-1) inappropriate ioctl for device
bash: no job control in this shell
When I start bash with strace, I get following output:
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
open("/dev/tty", O_RDWR|O_NONBLOCK) = -1 ENXIO (No such device or address)
ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
....
readlink("/proc/self/fd/0", "/dev/console"..., 4095) = 12
stat("/dev/console", {st_mode=S_IFCHR|0600, st_rdev=makedev(5, 1), ...}) = 0
open("/dev/console", O_RDWR|O_NONBLOCK) = 3
It looks, as if bash cannot open /dev/tty
. But /dev/tty
exists in /dev/
and has correct permissions:
ll /dev/tty*
crw-rw-rwT 1 root root 5, 0 2014-Sep-29 23:39:47 dev/tty
crw------T 1 root root 4, 0 2015-Dec-23 20:10:18 dev/tty0
crw------T 1 root root 4, 1 2015-Dec-23 20:10:18 dev/tty1
Why cannot bash
open /dev/tty
? And what does the ENXIO
error mean ?
Best Answer
As I said at https://unix.stackexchange.com/a/197472/5132,
init=/bin/sh
doesn't get "API" fileystems mounted, crashes in an ungainly fashion with no cache flush when one typesexit
(https://unix.stackexchange.com/a/195978/5132), and in general leaves it to the (super)user to manually do the actions that make the system minimally usable.One of those actions (if you want to use a job control shell, as you apparently do) is acquiring a controlling terminal.
/dev/tty
isn't an actual terminal device. It's a device that redirects to whatever the opening process' controlling terminal is. If it does not have one, as process #1 does not to begin with (and usually all of the time when a real system manager program is being run as process #1), then opening the device fails.Your system is too minimal. You need to run a program that sets up a controlling terminal, initializes a proper session, and probably does some of the bare minima of system management such as shutting down properly and cleanly, that then runs your job control shell.
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