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