182 lines
4.6 KiB
Groff
182 lines
4.6 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 chain
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mount real root filesystem and run its
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.Nm
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.It chain-merge
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complete a
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.Xr sysmerge 8
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upgrade during a chain boot
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.It multi-user
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boot to
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.Xr login 8
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.It single-user
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boot to root shell without password (not secure)
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.It sysinstall
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boot to operating system installer (not secure)
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.It 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 chain 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 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 "/etc/init/target" -compact
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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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