317 lines
7.6 KiB
Groff
317 lines
7.6 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 qsv
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.Op Fl \-target Ns "=" Ns Ar default-daemon
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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.
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.Pp
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Each
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.Xr daemon 7
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is started in order as its dependencies become ready per its
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.Xr init 5
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configuration.
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The
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.Sy default
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daemon is automatically started and its recursive dependencies constitute the
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operating system.
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The
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.Sy default
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daemon's single dependency is referred to as the target.
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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 itself as the intended system and complete
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the system startup.
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.Pp
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The options are as follows:
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.Bl -tag -width "12345678"
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.It Fl q , \-quiet
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Write status updates to the terminal only about failed daemons.
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This behavior is the default.
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.It Fl s , \-silent
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Never write status updates about daemons to the terminal.
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.It Fl t , \-target Ns "=" Ns Ar default-daemon
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Boot
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.Ar default-daemon
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as the target.
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The
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.Sy default
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daemon configuration is changed to only require the
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.Ar default-daemon
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dependency with the
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.Sy exit-only
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flag.
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.It Fl v , \-verbose
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Write all status updates about daemons starting and stopping to the terminal
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.El
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.Ss Cleanup of /tmp and /var/run
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.Nm
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deletes everything inside of
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.Pa /tmp
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if it exists, otherwise it is created with mode 1777.
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.Pp
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.Nm
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creates
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.Pa /var
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with mode 755 if it doesn't exist.
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.Nm
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deletes everything inside of
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.Pa /var/run
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if it exists, otherwise it is created with mode 755.
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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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If the target is
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.Sy chain
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or
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.Sy chain-merge ,
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then the real operating system is chain initialized.
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.Pp
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The root filesystem is mounted per
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.Pa /etc/fstab
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(see
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.Xr fstab 5 ) .
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This configuration file is a copy of the real file made by
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.Xr update-initrd 8
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when it makes the bootstrap
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.Xr initrd 7 .
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.Pp
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The root filesystem is found by searching each block device and partition.
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It is checked for consistency if necessary and mounted read-only if the check
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fails.
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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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If the target is
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.Sy chain-merge ,
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then the
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.Fl \-target=merge
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option is passed to the next
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.Nm .
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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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The filesystems are checked for consistency if necessary and mounted read-only
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if the check fails.
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.Ss Logging
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Logging to
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.Pa /var/log
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begins once the filesystems are mounted and
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.Nm
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writes the log entries from early boot to its
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.Pa /var/log/init.log .
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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 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 Merge
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If the target is
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.Sy merge ,
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then a delayed system upgrade is completed by invoking
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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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.Pp
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If the upgrade succeeds, the temporary
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.Pa /sysmerge/sbin/init
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deinitializes the system and invokes the real (now upgraded)
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.Pa /sbin/init ,
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which will restart system initialization in the normal fashion.
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.Ss Daemons
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The
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.Sy default
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.Xr daemon 7
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is started per its
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.Pa /etc/init/default
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.Xr init 5
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configuration file, which constitutes the operating system, and once it exits
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then
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.Nm
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exits with the same error code and the kernel shuts down the machine.
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The
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.Sy default
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daemon is meant to be a virtual daemon depending on a single top level daemon
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(the target), which provide the desired operating system functionality
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(e.g. booting to a single user shell or a multi user login screen).
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.Pp
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The daemons are configured per
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.Xr init 5
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where
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.Pa /etc/init
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contains the installation's local configuration, which overrides the operating
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system's default configuration in
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.Pa /share/init .
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The daemons are started in order as their dependencies become ready and are
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stopped in order when they are no longer required.
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.Pp
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The
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.Sy local
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daemon is meant to start the installation's local daemon requirements.
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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/
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Daemon configuration for the local system (first in search path) (see
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.Xr init 5 )
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.It Pa /etc/init/default
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Configuration for the default daemon (see
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.Xr init 5 )
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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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.It Pa /share/init/
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Default daemon configuration provided by the operating system (second in
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search path) (see
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.Xr init 5 )
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.It Pa /var/log/
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Daemon log files (see
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.Xr init 5 )
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.It Pa /var/log/init.log
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.Nm Ns 's
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own log.
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.El
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.Sh ASYNCHRONOUS EVENTS
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.Bl -tag -width "SIGUSR1"
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.It Dv SIGTERM
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Request system poweroff, normally sent by
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.Xr poweroff 8 .
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.It Dv SIGINT
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Request system reboot, normally sent by
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.Xr reboot 8 .
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.It Dv SIGQUIT
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Request system halt, normally sent by
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.Xr halt 8 .
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.It Dv SIGHUP
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Request system reinitialization.
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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 init 5 ,
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.Xr kblayout 5 ,
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.Xr videomode 5 ,
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.Xr daemon 7 ,
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.Xr initrd 7 ,
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.Xr kernel 7 ,
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.Xr halt 8 ,
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.Xr login 8 ,
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.Xr poweroff 8 ,
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.Xr reboot 8 ,
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.Xr sysmerge 8 ,
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.Xr update-initrd 8
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.Sh SECURITY CONSIDERATIONS
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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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