TTYs and Consoles

Syntax: tty [LVLS] <COND> DEV [BAUD] [noclear] [nowait] [nologin] [TERM]
tty [LVLS] <COND> CMD <ARGS> [noclear] [nowait]
tty [LVLS] <COND> [notty] [rescue]

The first variant of this option uses the built-in getty on the given TTY device DEV, in the given runlevels. DEV may be the special keyword @console, which is expanded from /sys/class/tty/console/active, useful on embedded systems.

The default baud rate is 0, i.e., keep kernel default.

The tty stanza inherits runlevel, condition (and other feature) parsing from the service stanza. So TTYs can run in one or many runlevels and depend on any condition supported by Finit. This is useful e.g. to depend on <pid/elogind> before starting a TTY.

Example:

tty [12345] /dev/ttyAMA0 115200 noclear vt220

The second tty syntax variant is for using an external getty, like agetty or the BusyBox getty.

The third variant is for board bringup and the rescue boot mode. No device node is required in this variant, the same output that the kernel uses is reused for stdio. If the rescue option is omitted, a shell is started (nologin, noclear, and nowait are implied), if the rescue option is set the bundled /libexec/finit/sulogin is started to present a bare-bones root login prompt. If the root (uid:0, gid:0) user does not have a password set, no rescue is possible. For more information, see the Rescue Mode section.

By default, the first two syntax variants clear the TTY and wait for the user to press enter before starting getty.

Example:

tty [12345] /sbin/getty  -L 115200 /dev/ttyAMA0 vt100
tty [12345] /sbin/agetty -L ttyAMA0 115200 vt100 nowait

The noclear option disables clearing the TTY after each session. Clearing the TTY when a user logs out is usually preferable.

The nowait option disables the press Enter to activate console message before actually starting the getty program. On small and embedded systems running multiple unused getty wastes both memory and CPU cycles, so wait is the preferred default.

The nologin option disables getty and /bin/login, and gives the user a root (login) shell on the given TTY <DEV> immediately. Needless to say, this is a rather insecure option, but can be very useful for developer builds, during board bringup, or similar.

Notice the ordering, the TERM option to the built-in getty must be the last argument.

Embedded systems may want to enable automatic DEV by supplying the special @console device. This works regardless weather the system uses ttyS0, ttyAMA0, ttyMXC0, or anything else. Finit figures it out by querying sysfs: /sys/class/tty/console/active. The speed can be omitted to keep the kernel default.

Most systems get by fine by just using console, which will evaluate to /dev/console. If you have to use @console to get any output, you may have some issue with your kernel config.

Example:

tty [12345] @console noclear vt220

On really bare bones systems, or for board bringup, Finit can give you a shell prompt as soon as bootstrap is done, without opening any device node:

tty [12345789] notty

This should of course not be enabled on production systems. Because it may give a user root access without having to log in. However, for board bringup and system debugging it can come in handy.

One can also use the service stanza to start a stand-alone shell:

service [12345] /bin/sh -l