Installation

NFS vs FTP

NFS and FTP (along with HTTP) are the three ways to install RedHat (as well as most other distributions of linux) over a network. The major difference between NFS and FTP is what they were originally intended for. NFS (Network File System) is designed to allow a remote user to mount a drive, similar to a local machine. Thus, it is optimized for frequent access and changes, all while being transparent (i.e., using the same commands as a local filesystem). FTP (File Transfer Protocol) is an Internet protocol used for the transfer of files. Since all we need to do is fetch a file, this is the preferred option for our setup. Actually, remnant makes the installation directory available for both FTP and NFS, from a common source.

Boot Floppies

The files in /images are disk images. The rawrite utility is used to copy the data directly to a floppy in DOS, similar to burning a CD using a .ISO (or a .CUE/.BIN combination). In linux, we can use a multipurpose tool, called dd. For more information on dd, check the man page, or just read the next paragraph.

A few notes on dd

Basics

Disk Duplicator (I guess... I dunno what it really stands for) is used to image things. That sentence (you know, the one with the really poor grammar) means to say that dd creates exact low-level copies. It works lower than the file system level, so the 1.44MB file that is a floppy image is an EXACT copy of the bits on the floppy disk. For making images, we do: dd if(inputfile)=<inputfilename> of(outputfile)=<outputfilename>. You don't actually need the count line.. it'll stop when it's finished. Note that by default, for archaic reasons, dd shows its results in 512 byte blocks... thus, doing a dd if=/dev/fd0 of=diskimage.img will says 2880 blocks done. That's not 2.88MB, it's 2.88 thousand 512B blocks = 1.44MB. Think about it if you're confused, but don't ask why ;). You can also tell it what size "chunks" to copy data in, by using the bs (block size) command. Count is a multiple of block size, so the following are all the same

dd if=/dev/fd0 of=image bs=1K count=100
dd if=/dev/fd0 of=image bs=10K count=10
dd if=/dev/fd0 of=image bs=100K count=1

Furthermore, all those will only image 100K worth of the file. Why you'd want to do this, I don't know, but that's what it'll do.

Interesting uses of dd

These are some dd uses.

Create a floppy image / restore a floppy image:

dd if=/dev/fd0 of=file.img 

dd of=/dev/fd0 if=file.img

Create an arbitrary sized file:

dd if=/dev/zero of=file # Don't do this! It'll run forever, or until 
the filesystem gets full

dd if=/dev/zero of=file bs=1M count=100 # 100 Meg file (all zeros). You 
can adjust bs and count to tweak performance... a good starting point 
might be 1K bs

Image copy of a hard disk (be careful using this for backups... do a google search first)

dd if=/dev/hda of=backupfile  # for a full disk
dd if=/dev/hda1 of=backupfile # just one partition

Hard drive wipe (see this story or this one about getting old data from hard drives)

dd if=/dev/urandom of=/dev/hda # Don't do this here!!!
dd if=/dev/zero    of=/dev/hda # Read up on why only zeros might not work 
as well, or ask me, if I'm in a good mood.

Back to Installation...

Passwords

RedHat's installer won't let you set the root password to a five character string... try a minimum of 6.

Config file notes

resolv.conf is for host name lookups (mapping names (e.g. remnant) to ip addresses (e.g. 192.168.5.250)). The search line tells it to try a default domain or rutgers.edu. That way, if you type ping eden, it'll try eden.rutgers.edu.

nsswitch tells the computer priorities in doing lookups. hosts: files dns means check the default files (that is, /etc/hosts), then do to the DNS servers listed in resolv.conf (128.6.238.13 and 128.6.224.114).

rpm-- too many options to list. Do a man rpm. One thing I will point out... usually, I do installs with a -Uvh, the U meaning Upgrade. That way, if a package is already installed, it'll update it nicely. However, for kernels, I strongly advise using -ivh. That way, it installs the new kernel adjacent to the current one, instead of overwriting the previous version. Very useful in case you want (need) to go back.

VI Note

If you're cutting and pasting the hosts file into vi, there's a good chance you'll wind up with everything on one line. Here's how to fix that. Read up on search and replace, but in a nutshell, this should do the trick:

:s/192/\r192/g

The :s is for replace (substitute, actually), the first argument is what to search for, the second is what to replace it with (the \r is a newline (aka return)), and the /g is for global, meaning everything on that line.

UPDATE- This is no longer true. We fixed the version on the website so you can cut and paste.. but this trick remains extremely useful.

Kickstart

Creating a boot disk

See above. Also, note that mcopy is (I guess) MSDOS Copy... that's why you give it a:. The other way to is mount /dev/fd0 /mnt/floppy, cp ks.cfg /mnt/floppy, umount /mnt/floppy. In linux, always unmount a floppy before removing it, otherwise you run the risk of data corruption. (In fact, I can almost guarantee that if you copy and eject promptly w/o unmounting, your file won't be there).

Booting

For a floppy kickstart, you start the linux kernel with the option ks=floppy. To automate this, look for an append line in the syslinux.cfg file. That way, you can have a kickstart with no keyboard interaction required (useful for clusters, where a machine might not have a keyboard or monitor).

anaconda-ks.cfg

As a safety feature, the parts about partitioning the hard disk in the automatic kickstart file are commented out. Make sure to remove the #'s if you want it to actually work.

Also, by default, the standard kickstart asks you to hit enter to reboot at the end. If you want completely unattended kickstarts, add the line "reboot" somewhere in your ks.cfg. Of course (and I learned this the hard way), you have to remove the floppy sometime during the kickstart (package installation is a safe time) so it doesn't reinstall over and over and over and over and over and over and i think i did that a few times myself... and over...

Finishing Up

Be advised that if you're confused about a file (say, lilo.conf), man is your friend (even if you're not a dog... I didn't say best friend). Not only can you do "man command", but "man filename" works too. Try a man lilo.conf to see the options available.

Finally

Just a reminder. Your text is VERY good... read it, learn it, memorize the %$#$ thing if you want. These notes are only what I think might be interesting side points as I read through the lecture notes (or based on comments I get from people during the Wednesday practical). They're not necessary relevant to passing the class, though to be a good admin, you should know all of this (and a heckuva lot more, too, of course).

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