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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 ?

Martin Vegter
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2 Answers2

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init is /bin/bash

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 types exit (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.

Further reading

Community
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JdeBP
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See What does the sh:cannot set terminal process group (-1) inappropriate ioctl for device error mean? for details on this error. As alluded to earlier, your environment is not correctly setup. In order for job control (foreground and background process handling) to work, your environment needs the calling process id, process group id, and session id to be set correctly. In addition, your process must have a tty, and it must be a controlling terminal.

The error you get indicates your process id, process group id, and session id are correct; because of the error you get. But, your shell is not the controlling terminal, hence the ‘-1’ error.

To set the tty to be the controlling terminal, you can use ioctl(your_fd, TIOCSCTTY,0) C API call in a program to do this.

eyoung100
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lazarus
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