removed '/etc/inittab' on a Linux host. As the following illustrates,
a missing 'inittab' really isn't as bad as it seems. Our details for
this setup are:
HOST: tux PROMPTS: [sh-3.2# |tux [0] ] OS: CentOS 5.4 LinuxWe start off with booting the host normally. As expected, we get through
the BIOS, we are presented with our GRUB options, and the default selection
(<===) is booted after the timeout:
GNU GRUB version 0.97 (639K lower / 1047488K upper memory) CentOS (2.6.18-164.el5) <=========================== CentOS Mirror (2.6.18-164.el5) Use the <up> and <down> keys to select which entry is highlighted. Press enter to boot the selected OS, 'e' to edit the commands before booting, 'a' to modify the kernel arguments before booting, or 'c' for a command-line. The highlighted entry will be booted automatically in 5 seconds. GRUB menu clears from the screen, and default option is booted: Booting 'CentOS (2.6.18-164.el5)' root (hd0,0) Filesystem type is ext2fs, partition type 0x83 kernel /boot/vmlinuz-2.6.18-164.el5 ro root=LABEL=/1 [Linux-bzImage, setup=0x1d00, size=0x1c31b4] initrd /boot/initrd-2.6.18-164.el5.img [Linux-initrd @ 0x37d73000, 0x27c402 bytes] <snip...> INIT: version 2.86 booting INIT: No inittab file found Enter runlevel:Above, we get partway through system bootup when 'init' errors, not
finding '/etc/inittab' and prompting us to select a runlevel. Our only
real option here is "s", or single user mode:
Enter runlevel: sAfter selecting the run level, we are dropped to a shell to start
resolving the situation. A quick check below verifies that '/etc/inittab'
doesn't exist. A further check of our mounted filesystems shows '/'
mounted. Time to fix '/etc/inittab':
sh-3.2# /bin/ls -ld /etc/inittab /bin/ls: /etc/inittab: No such file or directory sh-3.2# /bin/mount /dev/sda1 on / type ext3 (rw) proc on /proc type proc (rw) sysfs on /sys type sysfs (rw) devpts on /dev/pts type devpts (rw,gid=5,mode=620) /dev/sda2 on /var type ext3 (rw) tmpfs on /dev/shm type tmpfs (rw) none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw) sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw) mount: warning /etc/mtab is not writable (e.g. read-only filesystem). It's possible that information reported by mount(8) is not up to date. For actual information about system mount points check the /proc/mounts file. sh-3.2# echo "id:3:initdefault:" >> /etc/inittab sh: /etc/inittab: Read-only file systemUnfortunately, the error from our 'echo' statement tells us we should
have paid more attention to the output from 'mount'. With '/etc/mtab'
unwritable, the output from 'mount' is unreliable. We are actually
seeing stale data from '/etc/mtab'. Following as directed, we check
'/proc/mounts' and see that '/' is mounted read only. A quick remount of
'/' resolves this issue so we can create a new 'inittab':
sh-3.2# /bin/cat /proc/mounts rootfs / rootfs rw 0 0 /dev/root / ext3 ro,data=ordered 0 0 /dev /dev tmpfs rw 0 0 /proc /proc proc rw 0 0 /sys /sys sysfs rw 0 0 sh-3.2# /bin/mount -o remount,rw / EXT3 FS on sda1, internal journalUsing your favorite text editor (vi?), populate '/etc/inittab' with an
appropriate configuration. If this is a server, the following contents
are the minimum needed to get the host back up and functional:
sh-3.2# /bin/cat /etc/inittab id:3:initdefault: si::sysinit:/etc/rc.d/rc.sysinit l3:3:wait:/etc/rc.d/rc 3 l6:6:wait:/etc/rc.d/rc 6 1:2345:respawn:/sbin/mingetty tty1Of note, runlevel 6 is included because we will need it in a moment
to reboot the host. Without it, we'd get back deceptive messages that
processes are being killed. Without 'init' knowing what rc scripts to
call, not much is actually occuring to bring down the system, though
your terminal will likely hang. Additionally, we've configured a tty
on the last line so that when the host comes back up, we can log into
the box and do any additional cleanup. Without this line, no tty will
be spawned. When we reboot the host below, we get various errors though
these can be safely ignored for the moment:
sh-3.2# /usr/bin/reboot WARNING: could not determine runlevel - doing soft reboot (it's better to use shutdown instead of reboot from the command line) shutdown: warning: cannot open /var/run/shutdown.pid INIT: Switching to runlevel: 6 INIT: Sending processes the TERM signal INIT: Sending processes the KILL signal Starting killall: [ OK ] Sending all processes the TERM signal... [ OK ] touch: cannot touch `/var/lib/random-seed': No such file or directory chmod: cannot access `/var/lib/random-seed': No such file or directory Saving random seed: [FAILED] Syncing hardware clock to system time [ OK ] Turning off quotas: [ OK ] Please stand by while rebooting the system... md: stopping all md devices.Once shutdown is complete, the screen clears, the system resets, and the
system boots. While the system is coming up, you may see some messages
during the FS check like those below. These types of messages are fine:
<snip...> Setting up Logical Volume Management: [ OK ] Checking filesystems /1: Superblock last mount time is in the future. FIXED. /1: Superblock last write time is in the future. FIXED. /1: clean, 31367/1898688 files, 591969/1897670 blocks /var1: Superblock last write time is in the future. FIXED. /var1: clean, 972/524288 files, 34576/524120 blocks [ OK ] Remounting root filesystem in read-write mode: [ OK ] Mounting local filesystems: [ OK ] Enabling local filesystem quotas: [ OK ] Enabling /etc/fstab swaps: [ OK ] INIT: Entering runlevel: 3 <snip...> getty starts, screen clears, a login prompt is provided CentOS release 5.4 (Final) Kernel 2.6.18-164.el5 on an i686 tux login: _At this point, we can log in and, should we choose to do so, finish
customizing our 'inittab' file without any further downtime of the host.
Ideally, we would at least add in the rest of the runlevels (0-2,4,5),
and possibly a few more ttys. Since 'init' reads this file upon changing
to a new runlevel, no action is required for the runlevel changes.
To get 'init' to read the 'inittab' to spawn the newly added ttys,
run the following:
tux [0] /bin/ps -ef | /bin/grep g[e]tty root 2004 1 0 00:56 tty1 00:00:00 /sbin/mingetty tty1 tux [0] /bin/grep getty /etc/inittab 1:2345:respawn:/sbin/mingetty tty1 After adding ttys to 'inittab': tux [0] /bin/grep getty /etc/inittab 1:2345:respawn:/sbin/mingetty tty1 2:2345:respawn:/sbin/mingetty tty2 3:2345:respawn:/sbin/mingetty tty3 4:2345:respawn:/sbin/mingetty tty4 5:2345:respawn:/sbin/mingetty tty5 6:2345:respawn:/sbin/mingetty tty6 tux [0] /sbin/init q tux [0] /bin/ps -ef | /bin/grep g[e]tty root 2004 1 0 00:56 tty1 00:00:00 /sbin/mingetty tty1 root 2174 1 0 01:03 tty2 00:00:00 /sbin/mingetty tty2 root 2177 1 0 01:03 tty3 00:00:00 /sbin/mingetty tty3 root 2180 1 0 01:03 tty4 00:00:00 /sbin/mingetty tty4 root 2181 1 0 01:03 tty5 00:00:00 /sbin/mingetty tty5 root 2182 1 0 01:03 tty6 00:00:00 /sbin/mingetty tty6
