Network Setup

All our machines are on a subnet of 192.168.5.x. The gateway machine, which is named capone, has two network cards. Do an ifconfig to see how it's set up (this may not be in your path... try whereis ifconfig or locate ifconfig first). This also protects our local machines, and allows us to have really cheesy root passwords without worrying about someone cracking into them.

Basic Commands


In case you don't know already, eXecute permission on a directory means you can change to it. chmod can be used with letters (a+x for all (who) can execute (what)), or numbers. Give it a 3 digit octal number, where the first number signifies the owner, the second the group, and the third everyone else. Each number is 0-7, depending on whether you want r,w, and/or x. To get a number, start with 0. Add 4 for read permission, 2 for write, and 1 for execute. Thurs, rwx is 7, r-x is 5, and r-- is 4. Try and see if --x (1) makes sense... can you execute a file you can't read?


With regard to redirecting stdout and stderr, this is often helpful to pause long displays from make, where stuff often gets written to stderr, and thus cannot be paginated with less (or more, or most, alternative pagers). Also, if you want a command to be silent, try sending it to /dev/null (the big bit in the sky, aka, bit heaven/hell). command 2>&1 > /dev/null will be completely silent, whereas command > /dev/null will only silence the messages printed to stdout.

When redirecting, note the following.
Symbol  If output existsIf output doesn't exist
|Output to a file (must exist)N/A
>Overwrite a fileCreate a file
>>Append to a fileCreate a file

Searching with Grep

grep is an interesting tool. It's one of the most useful tools... it searches for a given string. Couple of examples:
grep test * # searches for the string "test" in all files in the current 
grep test -r * # searches for the string "test" in all files in the current directory and below (recursive)
grep 'te.t' * # matches test, tent, and anything with te, a character, then another t. Look up regular expressions to learn more
grep test < filename # searches in "filename" Note that for one file, you have to redirect it in.
ls -l | grep test # searches for files with test in the name (could be done using find, as well).
grep -i # case insensitive
grep -v # searches for files (lines) NOT containing the given string.

Disk Partitions


Disk partitioning in linux works a bit differently than in windows. In linux, you partition each drive into multiple partitions, which are then mounted at various points. Each physical hard drive has an entry in /dev/, which is either hdXX for IDE drivers, or sdXX for SCSI's. The first X is a letter from a - something, depending on where it is connected to the motherboard. The primary master is a, the primary slave is b, the secondary master is c, etc. The second X is the partition number. For example, the 3rd partition on the primary slave drive is hdb3.

Mounting, and Common Directories

One file system must contain the root filesystem, aka, be mounted as slash. On many of our machines, that's hda2. (To see the mount points, type mount, or type df). Then, other partitions can be mounted at various points. For example, on most of these machines, hda1 is mounted on /boot. Note that there needs to be a directory called /boot on / in order to mount something there.

Common directories to put on their own partition are /boot, /usr, /home, /var, and /tmp. Boot often gets it's own, tiny, partition, to aid it keeping booting compatible (many older boards could only boot from the first 1024 clusters). /usr is where the majority of executables reside, and needs a good chunk of space. /home is where most home directories are kept, and should be saved during system upgrades, and backed up frequently. /var is often seperated to prevent runaway logs (or mail spools, in /var/mail or /var/spool/mail from filling the entire system). Finally, a lot of people keep /tmp seperate, both to limit temp file size, and for security reasons. That reasoning goes as follows. Users have to be able to write to /tmp, but an admin might be wary of a user compiling a malicious program and leaving it in /tmp to be run by an unsuspecting victem. They will therefore mark /tmp as noexec, meaning nothing can be executed from within /tmp.

Special Directories

lost+found exists in the root directory of every partition. To see how a hard drive is partitioned, look at the output of df.
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