What to do when new kernel does not work

Ocassionally things go bad(tm). This has bit me for the second time in approx 3 years now, but generally one needs to load the old FreeBSD kernel to start debugging and going through a box with a fine toothcomb.

The following snipbit gives you an idea what steps to take when rebooting the server so that you can load the previous working copy of the FreeBSD kernel:
When the boot menu appears hit the spacebar to stop the countdown.
Press "6" for "to escape to loader prompt"
unload
load /boot/kernel.old/kernel
boot

Now the old working FreeBSD kerenl is booting up. It would be recommended to copy the last working version to /boot/kernel.last for example so that you can "load /boot/kernel.last/kernel", especially if you are going to be building your kernel multiple times on a server.

Cron zombie killer

This searches for and destroys the zombie processes that linger (and block I/O for an indefinite amount of time) after cron starts up on a shared server:

for each in `ps jauxww | grep Z | grep -v PID | awk '{print $3}'`; do for every in `ps auxw | grep $each | grep cron | awk '{print $2}'`; do kill -9 $every; done; done

exim router for relaying via a smarthost

User the "begin routers" section add:

route_append:
    driver = manualroute
    domains = *
    transport = remote_smtp
    route_data = "smarthost.host.name byname"

Formatting a disk for use in FreeBSD

Given that this isn't something I do regularly, it's handy to have the commands to hand so I don't have to scroll through man pages trying to remember how to do it.

Clear the disk

# dd if=/dev/zero of=/dev/ad1 bs=1k count=1

Initialise it

# fdisk -BI ad1

Label it, then edit the labels created

# bsdlabel -B -w ad1s1 auto
# bsdlabel -e ad1s1

Format it with a filesystem

# newfs /dev/ad1s1e

Make directories and mount as appropriate, and you're done!

Upgrading a kernel

Install CVSup

cd /usr/ports/net/cvsup-without-gui
make install distclean

Make and populate the CVSup config file

touch /root/cvsup-stable-src.sup
echo '*default host=cvsup14.us.FreeBSD.org' >> /root/cvsup-stable-src.sup
echo '*default base=/var/db' >> /root/cvsup-stable-src.sup
echo '*default prefix=/usr' >> /root/cvsup-stable-src.sup
echo '*default release=cvs tag=RELENG_5' >> /root/cvsup-stable-src.sup
echo '*default delete use-rel-suffix compress' >> /root/cvsup-stable-src.sup
echo ' src-all' >> /root/cvsup-stable-src.sup

Update the /usr/src/ tree

cvsup /root/cvsup-stable-src.sup

Get rid of any old "worlds" and make a new one

rm -rf /usr/obj/usr
cd /usr/src/
make buildworld

Make changes to /usr/src/sys/i386/conf/GENERIC and name it was what you want.

Build the kernel, install the kernel, verify it and dot.old in /boot/, run mergemaster, and install the new world.

make buildkernel KERNCONF=GENERIC
make installkernel KERNCONF=GENERIC
mergemaster -p
make installworld
mergemaster
ls -l /boot/
shutdown -r now

Note, we often run in a securelevel of 1 and have immutable binaries in the system folders. You'll need to edit rc.conf.

nano /etc/rc.conf

kern_securelevel_enable="NO"
kern_securelevel="1"

Reboot

shutdown -r now

Then make things mutable

chflags noschg /bin/*
chflags noschg /sbin/*
chflags noschg /bin
chflags noschg /sbin
chflags noschg /usr/bin/*
chflags noschg /usr/sbin/*
chflags noschg /usr/bin
chflags noschg /usr/sbin

Using pw to add a group and user in FreeBSD

Using "textdrive" as an example

pw groupadd textdrive
pw useradd textdrive -m -c "Main Textdrive account" -d /home/textdrive -s /bin/tcsh -G textdrive -k /usr/share/skel/

Then set the password:

passwd textdrive