Introduction to FreeBSD Additional Topics

PacNOG I Workshop

June 20, 2005 Nadi, Fiji

Hervey Allen

Topics
How FreeBSD boots (more detail) Recompiling the FreeBSD kernel Kernel loadable modules and hardware support Firewalls X Window vs. Gnome vs. KDE cvs in detail FreeBSD file system: UFS Logs Use of su crontab Lots more commands

How FreeBSD Boots

Initial boot items are in /boot (this resides under /, or in it's own partition). boot0:
Copy of MBR is in /boot/boot0. MBR is at start of the boot disk and is 512 bytes in size. If you use lilo, grub, or other MBR then this is not relevant.
boot1/boot2 or Stage 1 and 2:
/boot/boot1 is 512 bytes in size and runs /boot/boot2. /boot/boot2 is more complex and runs / boot/loader.

How FreeBSD Boots cont.

Stage 3 or /boot/loader:
Probes for consoles and disk Reads in this order: /boot/loader.rc /boot/defaults/loader.conf /boot/loader.conf to override previous Kernel and modules are loaded after a 10 second wait for key press. Interactive prompt available. For more discussion and examples see:
http://www.freebsd.org/doc/en_US.ISO88591/books/handbook/boot-blocks.html

The init process:

After the kernel boots it hands over control to the user process /sbin/init. If filesystems look good then init begins reading the resource configuration of the system. These files are read in this order: /etc/defaults/rc.conf /etc/rc.conf (overrides previous) /etc/rc.conf.local (overrides previous) Mounts file systems in /etc/fstab

The init process cont.:

Once file systems are mounted then the following starts: Networking services System daemons Locally installed package daemons (/usr/local/etc/rc.d scripts)
Init process and shutdown:
When shutdown is called then init runs the scripts /etc/rc.shutdown.

The FreeBSD Kernel

You might rebuild a kernel to add hardware support, additional filesystem support, etc. Kernel source, if installed, is in /usr/src/sys
If there is not a /usr/src/sys directory on your system, then the kernel source has not been installed. The easiest way to do this is by running /stand/sysinstall as root, choosing Configure, then Distributions, then src, then sys. (FreeBSD Handbook 9.3)
To rebuild your kernel you use the default configuration file, update settings as needed, then recompile the kernel, installing it in /boot.
Recompiling the FreeBSD Kernel
See FreeBSD Handbook section 9.3 Config file in /usr/src/sys/arch/conf Example (old style):
cp GENERIC /root/kernel/MYNEWKERNEL ln -s /root/kernel/MYNEWKERNEL /usr/sbin/config MYNEWKERNEL cd./compile/MYNEWKERNEL make depend, make, make install
Recompiling the FreeBSD Kernel cont.

Example (new style):

cd /usr/src make buildkernel kernconf=MYNEWKERNEL make installkernel kernconf=MYNEWKERNEL
Kernel installed as /boot/kernel Old kernel is in /boot/kernel.old If new kernel does not boot, go to boot loader prompt and type:

unload boot kernel.old

The kernel config file has many options. For a more complete explanation of the various options see (e.g. on a PC with Intel CPU):
/usr/src/sys/i386/conf/NOTES
Or look at the FreeBSD Handbook section 9.4 for some more examples.
Kernel and Hardware Support
FreeBSD is moving towards modularizing hardware support. That is drivers (kernel loadable modules) are loaded at boot time to support your systems' hardware. Some hardware is still supported by statically loaded software directly in the kernel. Some hardware use is optimized by setting kernel state using the sysctl facility.
Kernel Loadable & Static Modules
Static (in conf) built-in during recompile vs. Kernel loadable (kld) /boot/kernel modules. Autoloading using /etc/rc.conf directives and/or using /boot/loader.conf, which overrides /boot/defaults/loader.conf Address security in FreeBSD vs. Linux and modules.
Commands kldload, kldstat, kldunload

Firewalls

Building an appropriate firewall ruleset for your situation requires thought:
See FreeBSD Handbook section 10.8 to get started. Enable IP FireWall support (IPFW) by adding one, or more options to kernel configuration file. ipfw was updated to ipfw2 in July 2002. Starting and stopping in /etc/rc.conf and /etc/rc.firewall. ipfw rules and firewall set are in /etc/rc.firewall. You can dynamically control ipfw as well: ipfw flush, ipfw enable, ipfw disable, ipfw flush, etc.

Installing a Binary File

This is much less common, but you can precompile a program for a specific version of FreeBSD. Clearly this would be something that might be done with commercial applications that have restrictive licensing agreements. Normally installation is done using a shell script that copies compressed files to the appropriate locations and updates configurations as needed. Adobe's Acrobat Reader, Macromedia Flash plugin, etc. are examples (/usr/local/bin/acroread).

Installing with CVS

CVS: Concurrent Versions System Somewhat detailed FreeBSD Handbook entry: http://www.freebsd.org/doc/en_US.ISO88591/books/handbook/cvsup.html Typical use for CVS and FreeBSD (other than software projects) is to keep your Ports collection up-to-date. To do this be sure you have installed the Ports collection at initial installation. Now install cvsup-without-gui from source if necessary:

Install cvsup

If you are using KDE or Gnome, then check:

pkg_info | grep cvs

If CVS is installed you can skip this. Otherwise:
cd /usr/ports/net/cvsup-without-gui or cd /usr/ports/net/cvsup make make install make clean

Install cvsup cont.

Now copy the cvsup configuration file needed to tell CVS to upgrade your ports collection. A sample is located in /usr/share/examples:
cp /usr/share/examples/cvsup/ports-supfile /root/.
Edit this file to look like this (line 50):
# IMPORTANT: Change the next line to use one of the CVSup mirror sites # listed at http://www.freebsd.org/doc/handbook/mirrors.html. *default host=cvsup.th.FreeBSD.org *default base=/usr *default prefix=/usr *default release=cvs tag=. *default delete use-rel-suffix

Install and Use cvsup

At this point you are ready to update your entire Ports collection with one simple command:
cvsup -g -L 2 /root/ports-supfile
-g : don't use graphical interface. -L 2 : verbosity level. Level 2 is verbose.

CVS Summary

CVS is a powerful and complex tool. For some more hints and information see: man cvsup info cvs FreeBSD Handbook:
http://www.freebsd.org/doc/en_US.ISO88591/books/handbook/ports-using.html

X Windows Gnome KDE

The first thing to understand is that Gnome and KDE use the X graphical subsystem. Generally KDE programs run in Gnome and vice-versa. For a server you do not need to run, or install, any of these. You can run one, both, or other window managers like fwvm, windowmaker, etc.

X Gnome KDE cont.

Which desktop environment is better? There's no correct answer to this. To configure how X runs you specify this in the file /etc/X11/xorg.conf. You general configure using the command: Xorg -config To exit X you can press ALT-CTRL-Backspace. You can, also, go directly to a terminal using altctrl-f1 through f8. alt-ctrl-f9 returns to X.
The FreeBSD Unix File System

Taken from Wikipedia:

UNIX file system (UFS) is a file system used by many unix operating systems. It is derived from the Berkeley Fast File System (FFS), which itself was originally developed from FS in the first versions of UNIX developed at Bell Labs. Nearly all BSD unix derivatives including FreeBSD, NetBSD, OpenBSD, NeXTStep, and Solaris use a variant of UFS. In Mac OS X it is available as an alternative to HFS. In Linux, partial UFS support is available and the native linux ext2 filesystem is derived from UFS.

FreeBSD UFS cont.

UFS2 and Soft Updates make for a powerful combination:
Data is clustered on cylinders to reduce fragmentation. Block level fragmentation to avoid wasting disk space when large block sizes are used. Extended attribute support. Support for 1TB file systems. Fast file system creation using lazy inode initizializtion. Soft updates to dramatically improve metadata operations. UFS is journaled so no need for fsck on large drives.
To learn more about UFS and Soft Updates:
UFS Definition from Wikipedia: http://en.wikipedia.org/wiki/UFS Little UFS2 FAQ: http://lists.freebsd.org/pipermail/freebsd-current/2003April/001444.html Disk Tuning (Soft Udpates): http://www.freebsd.org/doc/en_US.ISO88591/books/handbook/configtuning-disk.html#SOFT-UPDATES Inode Definition from Wikipedia: http://en.wikipedia.org/wiki/Inode
DEVice File System: Basically a way to interact with new devices at the kernel level in the global file system namespace. DEVFS allows the sytem to adapt to hardware changes more cleanly. USB, firewire, etc. device mounts are cleaner. Included by default in FreeBSD 5.0 and above.
No longer need to use makedev to create device nodes for new hardware.
Installing FreeBSD (5.2.1)

Sample install session.

Boot from CD-ROM Pick default FreeBSD install Choose Express install option Delete any slices laying around Use "A" (entire disk) for FreeBSD slice Q to finish disk partition Install FreeBSD BootMgr Create partitions like this: - / 1GB - /var 1GB with SoftUpdate on - swap 1GB - /usr (rest of disk with Softupdates on) Q to finish partition creation Choose A, or All to install everything Choose to install Ports Click Exit twice to get to media dialogue Choose to install from CD/DVD Say "Yes" to last chance to set options - set root password - add users - configure addtion network interfaces - configure dc0 - no dhcp - host = int/labnn - domain = workshop.th - ipv4 gw = 203.159.31.1 - nameserver = 203.159.0.1 - ipv4 address = 203.159.31.nnn - netmask (calc) = 255.255.255.0 - configure your mouse, turn on mouse daemon - Configure Gnome - Get from CD/DVD - Add package bash - install packages - shells - Add package sudo (under security) - Set timezone remove CD-ROM reboot

Installing FreeBSD cont.

First pick the type of install:
- Standard - Express - Custom
During install you must partition and slice. After install use Configure to:
Install Distribtutions Packages Configure network, accounts, Timezone, mouse, etc.

More Commands

ps cat less more tail gzip gunzip tar grep ProceSs list. Show information for running processes ConCATenate a file to the default ouput (screen) Display file pausing each page & allowing movement Display file pausing each page, but no movement Display the end of a file (see -f option) Compress file(s) using Lempel-Ziv coding Decompress zip'ped files Manipulate Tape ARchive files. Search text/files for patterns (many variations)
bunzip2 Uncompress files compressed with bzip2

Even More Commands

gcc mount* apropos hexdump netstat bg history nmap** bzip2 id ping chgrp* ifconfig* pkg_add chmod info pkg_delete clear init* pkg_info chown* kill printenv ctrl-u ln ps date locate pwd exec lsof** reset df mkdir route* dmesg | pipe rmdir du man script export mkisofs set file find *root only for changes **Not installed by default in FreeBSD

su sysinstall sysctl swapinfo tcpdump top touch traceroute uname unset unzip users watch whereis which whoami

Basic vi Commands

Impress your friends. Open: vi fn, vi -r fn, vi + fn, vi +n fn, vi +/pat fn Close: :w, w!:, :wq, :wq!, :q, :q! Movement: h,j,k,l w, W, b, B, :n (+arrow keys) Edit: A, i, o, x, D, dd, yy, p Search: /pattern, ?pattern, n, N

/etc/group

Format is:
wheel:*:0:root,hervey,test
Group name. 8 characters or less. Encrypted password. Rarely used. * as placeholder. Group Identifying number (GID). List of group members seperated by commas. User's login shell.

Using the su Command

The su command is used to become a different userid, like root, without having to logout and log back in. To use su to become root your userid has to be given permission to do this in /etc/sudoers. You can allow users to run specific privileged commands using /etc/sudoers and sudo. You can assign users to the wheel group and using /etc/sudoers you can allow them to run all commands (or some, but unusual). Use visudo as root to allow users or groups to use sudo. Users in the wheel group can run su.

More Uses for the su Command
Instead of having to open a root shell, you can run a privileged command like this:

sudo command

For example:

sudo mount /mnt/cdrom

And, if you wish to open a different user shell and run their login scripts do:

su userid

Looking for More Information
Not only can you use commands to find information about your system, but you can look inside several files, and you can use the sysctl facility as well. Example of files with useful information: /etc/motd /etc/resolve.conf /etc/services /etc/X11/xorg.conf /etc/fstab

More information cont.

If you are used to /proc it's possible to compile support for this in to the kernel, but not normally used (options LINPROCFS in kernel conf file). You can look in /boot/kernel for modules available and use kldstat to see what's loaded (kernel loadable modules = kld). Use dmesg to see what is reported during startup, including hardware and addresses. Use of sysctl, such as: sysctl -a, sysctl -aN sysctl kern.maxproc And, see /etc/sysctl.conf
Logs How to Know What's Up
To configure what happens to events that are logged by applications using syslog, edit the file /etc/syslog.conf (see man syslog.conf). Take a look at the file /var/log/messages. The tail command is very useful for this. To troubleshoot start by typing: tail -f /var/log/messages and in another terminal start and stop the service you are trying to debug.

Logs cont.

There are many log files. For example, if you run a webserver, like apache, all of the webserver logs are likely to be in /var/log/httpd sendmail uses /var/log/maillog There are multiple software packages to read and automatically generate reports based on logfiles. See: http://nsrc.org/security/index.html#logging for some examples of available packages.

Mounting Filesystems

If you want to mount a filesystem not listed in /etc/fstab then you need to use the mount command. First, you need to know what entry in the /dev directory describes the device you wish to mount (a cd, floppy, another hard drive, etc.). You, also, need to know what type of filesystem. For example, mounting a dos formatted floppy: mount -t msdos /dev/fd0 /mnt/floppy or

mount_msdosfs /dev/fd0 /mnt/floppy mount -t msdos /dev/da0s1 /mnt/usb
And, a USB flash pen drive:

Crontab

The cron service allows you to automatically run programs when you want. This is configured in /etc/crontab, and /var/cron/tabs/ Use the command crontab in order to change the files that control how the cron daemon works.

Crontab cont.

In addition you can specify who may and may not use cronjobs with /var/cron/allow and /var/cron/deny
A cron file that shows how a service is going to run has the following format:
Minute Hour Day Month Weekday Command

An example:

* /bin/mail user@dot.com < /home/user/joke
Send an email on the first of April.