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The bootloader will now load the /boot/random.seed file if it exists, in which case the kernel will use it as the initial kernel entropy. The kernel warns if no random seed was loaded, unless the --no-random-seed option was given. This option is used for live environments that inherently have no prior secret state. The kernel initializes its entropy pool from the random seed as of the first things, so randomness is available very early on. init(8) will emit a fresh /boot/random.seed file on boot to avoid the same entropy being used twice. init(8) also writes out /boot/random.seed on system shutdown where the system has the most entropy. init(8) will warn if writing the file fails, except if /boot is a real-only filesystem, and keeping such state is impossible. The system administrator is then responsible for ensuring the bootloader somehow passes a fresh random seed on the next boot. /boot/random.seed must be owned by the root user and root group and must have file permissions 600 to avoid unprivileged users can read it. The file is passed to the kernel by the bootloader as a multiboot module with the command line --random-seed. If no random seed is loaded, the kernel attempts a poor quality fallback where it seeds the kernel arc4random(3) continuously with the current time. The timing variance may provide some effective entropy. There is no real kernel entropy gathering yet. The read of the CMOS real time clock is moved to an early point in the kernel boot, so the current time is available as fallback entropy. The kernel access of the random seed module is supposed to be infallible and happens before the kernel log is set up, but there is not yet a failsafe API for mapping single pages in the early kernel. sysupgrade(8) creates /boot/random.seed if it's absent as a temporary compatibility measure for people upgrading from the 1.0 release. The GRUB port will need to be upgraded with support for /boot/random.seed in the 10_sortix script. Installation with manual bootloader configuration will need to load the random seed with the --random-seed command line. With GRUB, this can be done with: module /boot/random.seed --random-seed
221 lines
5.4 KiB
Groff
221 lines
5.4 KiB
Groff
.Dd $Mdocdate: 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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.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. 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. If the
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system is bootable cdrom, then the initrd will be a fully functional system and
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.Nm
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will start a live environment or an operating system installer. If the
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system is installed on a harddisk, then the initrd is a minimal system 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. The next
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stage init will recognize it as the intended system and complete the system
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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. 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. The kernel command line can specify the path to
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.Nm
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and its arguments. Unprivileged users can change the kernel command line from
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the bootloader command line if it hasn't been password protected. Likewise
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unprivileged users can use their own replacement bootloader by booting a
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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) and runs the next
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.Nm
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program. 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. It is checked for consistency if nessesary. It is
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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 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. The file is also written on system shutdown where the
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system has the most 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. 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. This will
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be a login screen, a root shell, or something else. If the process exits
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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
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normally. The kernel decides whether to power off, reboot or halt based on this
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exit 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. Any other exit by the
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initial
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.Nm
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will trigger a kernel panic.
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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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