.Dd October 5, 2015
.Dt INIT 8
.Os
.Sh NAME
.Nm init
.Nd system initialization
.Sh SYNOPSIS
.Nm init
.Op Fl \-target Ns "=" Ns Ar init-target
.Op Fl \-
.Op Ar chain-init ...
.Sh DESCRIPTION
.Nm
is the first program run after system startup and is responsible for
initializing the operating system and starting the specified
.Ar init-target .
This is normally a login screen, a root shell, or a dedicated special purpose
program.
.Pp
The
.Xr kernel 7
starts the system in a temporary environment with a root filesystem
backed by system memory and extracts the
.Xr initrd 7
into it.
The kernel runs the
.Pa /sbin/init
program of the system memory root filesystem as the first process.
If the system is on bootable cdrom, then the initrd will be a fully functional
system and
.Nm
will start a live environment or an operating system installer.
If the system is installed on a harddisk, then the initrd is a minimal system
made with
.Xr update-initrd 8
that will search for the actual root filesystem and chain init it.
The next stage init will recognize it as the intended system and complete the
system startup.
.Ss Initialization Target
.Nm
first determines its target from the
.Fl \-target
option if specified or
.Pa /etc/init/target
otherwise.
Supported targets are:
.Pp
.Bl -tag -width "single-user" -compact -offset indent
.It Sy chain
mount real root filesystem and run its
.Nm .
.It Sy chain-merge
like
.Sy chain
but run
.Pa /sysmerge/sbin/init
with the
.Sy merge
target.
.It Sy merge
finish a
.Xr sysmerge 8
upgrade and then execute the real
.Nm
with its default target.
.It Sy multi-user
boot to
.Xr login 8 .
.It Sy single-user
boot to root shell without password (not secure).
.It Sy sysinstall
boot to operating system installer (not secure).
.It Sy sysupgrade
boot to operating system upgrader (not secure).
.El
.Pp
It is a full system compromise if unauthenticated users are able to boot the
wrong target.
The kernel command line can specify the path to
.Nm
and its arguments.
Unprivileged users can change the kernel command line from the bootloader
command line if it hasn't been password protected.
Likewise unprivileged users can use their own replacement bootloader by booting
a portable device under their control if the firmware configuration has not been
password protected.
.Ss Partition Creation
.Nm
will scan every block device for valid partition tables and create the
corresponding partition devices in
.Pa /dev .
.Ss Chain Initialization
The
.Sy chain
target mounts the root filesystem as in
.Pa /etc/fstab
(see
.Xr fstab 5 )
and runs the next
.Nm
program.
This is used by
.Xr update-initrd 8
to make a bootstrap
.Xr initrd 7 .
.Pp
Every block device and partition is scanned to determine if it is the root
filesystem.
It is checked for consistency if necessary.
It is mounted at
.Pa /tmp/fs.XXXXXX
and the
.Pa /dev
filesystem directory is bound at
.Pa /tmp/fs.XXXXXX/dev .
.Pp
Finally the
.Pa /sbin/init
program (or
.Ar chain-init
if specified) of the target root filesystem is run inside a chroot.
.Ss Configuration
Once the
.Nm
of the real root filesystem runs, it will process basic configuration files and
apply them:
.Pp
.Bl -tag -width "/etc/videomode" -compact -offset indent
.It Pa /etc/hostname
set hostname (see
.Xr hostname 5 )
.It Pa /etc/kblayout
set keyboard layout (see
.Xr kblayout 5 )
.It Pa /etc/videomode
set graphics resolution (see
.Xr videomode 5 )
.El
.Ss Mountpoints
.Nm
mounts all the filesystems according to
.Xr fstab 5 .
.Ss Random Seed
.Nm
will write 256 bytes of randomness to
.Pa /boot/random.seed ,
which serves as the initial entropy for the
.Xr kernel 7
on the next boot.
The file is also written on system shutdown where the system has the most
entropy.
.Ss Merge
The
.Sy merge
target completes a delayed system upgrade by invoking the
.Xr sysmerge 8
at
.Pa /sysmerge/sbin/sysmerge
with the
.Ar --booting
option.
If the upgrade succeeds, the temporary
.Nm
deinitializes the system and invokes the real (now upgraded)
.Nm
which will restart system initialization in the normal fashion.
.Ss Session
Finally
.Nm
will start the target program according to its initialization target.
This will be a login screen, a root shell, or something else.
If the process exits abnormally
.Nm
will automatically restart it.
.Nm
will exit with the same exit status as the process if it exits normally.
The kernel decides whether to power off, reboot or halt based on this exit
status.
.Sh ENVIRONMENT
.Nm
sets the following environment variables.
.Bl -tag -width "INIT_PID"
.It Ev HOME
root's home directory
.It Ev INIT_PID
.Nm Ns 's
process id
.It Ev LOGNAME
root
.It Ev PATH
.Pa /bin:/sbin
.It Ev SHELL
root's shell
.It Ev TERM
sortix
.It Ev USER
root
.El
.Sh FILES
.Bl -tag -width "/boot/random.seed" -compact
.It Pa /boot/random.seed
initial kernel entropy
.It Pa /etc/init/target
default initialization target
.It Pa /etc/fstab
filesystem table (see
.Xr fstab 5 )
.It Pa /etc/hostname
hostname (see
.Xr hostname 5 )
.It Pa /etc/kblayout
keyboard layout (see
.Xr kblayout 5 )
.It Pa /etc/videomode
graphics resolution (see
.Xr videomode 5 )
.El
.Sh EXIT STATUS
.Nm
exits 0 if the kernel should power off, exits 1 if the kernel should reboot, or
exits 2 if the boot failed and the kernel should halt with a complaint about an
.Nm
fatality.
Any other exit by the initial
.Nm
will cause the kernel to halt with a complaint about an unexpected exit code.
.Nm
exits with the same exit status as its target session if it terminates normally.
.Sh SEE ALSO
.Xr fstab 5 ,
.Xr hostname 5 ,
.Xr kblayout 5 ,
.Xr videomode 5 ,
.Xr initrd 7 ,
.Xr kernel 7 ,
.Xr login 8 ,
.Xr sysmerge 8 ,
.Xr update-initrd 8