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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](rescue.md) 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
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