A brief introductions to the intricacies of Archlinux

Question

_JeffG_ 's post gave me an idea to start this... i know the developers are busy, so I figured we could start a thread here with the intricasies of how ArchLinux is set up. For example; I've spont a lot of time in /etc/ so here's what I've found out:
/etc/pacman.conf
Repositories
This is the configuration file for pacman. the package manager for achlinux.
As per default you can only access packages in the 'official' repository.  To gain access to the multitude of packages available in the unofficial repository look around line 48, there will be a section that looks like:
# Uncomment this block to access the 'unofficial' package set
[unofficial]
#Server = ftp://ftp.ibiblio.org/pub/linux/distributions/archlinux/unofficial
#Server = ftp://ftp.webtrek.com/pub/mirrors/archlinux/unofficial
#Server = ftp://ftp.archlinux.org/unofficial
#Server = ftp://ftp.mpi-sb.mpg.de/pub/linux/mirror/ftp.ibiblio.org/pub/Linux/distributions/archlinux/unofficial
#Server = ftp://ftp.oit.unc.edu/pub/Linux/distributions/archlinux/unofficial
#Server = ftp://ftp.tu-chemnitz.de/pub/linux/sunsite.unc-mirror/distributions/archlinux/unofficial
#Server = ftp://ftp.parrswood.net/Mirrors/ftp.archlinux.org/unofficial
#Server = ftp://gd.tuwien.ac.at/opsys/linux/archlinux/unofficial
#Server = ftp://saule.mintis.lt/pub/linux/unofficial
#Server = ftp://ftp.rez-gif.supelec.fr/pub/Linux/distrib/archlinux/unofficial
Uncomment (remove the # marks) that section to gain access to the unofficial repository.
Note: there are also 'stable' and 'unstable' repositories as well, read the short documentation in the file for information on those.
Also Note: User-created packages are available at ftp://ftp.archlinux.org/incoming/.  It is common practice to post here: http://bbs.archlinux.org/viewforum.php?f=25 when a new package is submitted.
Options
At the beginning of the /etc/pacman.conf file is the options section, which by default looks like:
# GENERAL OPTIONS
[options]
NoUpgrade = etc/passwd etc/group etc/shadow
NoUpgrade = etc/fstab etc/rc.conf etc/rc.local
NoUpgrade = etc/lilo.conf etc/raidtab
#IgnorePkg = lilo gcc
It is in this section we can setup a few more options for pacman.  Here is a list of currenty available options:
  DBPath = /path/to/db/dir
         Overrides the default location of the toplevel  database  direc-tory.  The default is /var/lib/pacman.
   IgnorePkg = <package> [package] ...
          Instructs  pacman  to  ignore any upgrades for this package when performing a --sysupgrade.
   NoPassiveFtp
          Disables passive ftp connections when downloading packages. (aka Active Mode)
   NoUpgrade = <file> [file] ...
          All  files  listed  with  a  NoUpgrade  directive  will never be touched during a package install/upgrade.  Note: do not  include the leading slash when specifying files.
NoUpgrade is what you would use for system critical config files and whatnot.
How pacman deals with config files
This is my understanding from experience (and the manpage) with how pacman will handle config files under different cases.
1) Removing a package
Pacman creates a backup of the config file with a .pacsave extension.  For example, when i installed metalog and removed syslog, pacman moved /etc/syslog.conf to /etc/syslog.conf.pacsave
2) Upgrading a package (heres the tricky part)
pacman uses creates three md5sums to figure out what to do.
md5sum #1 = original config file in the original package installed before the upgrade
md5sum #2 = current config file thats actually in use by the system
md5sum #3 = new config file with the updated package that is not yet installed
if original == current == new (e.g. all files are the same) then the new one is isntalled
if (original == current) != new (e.g. original config was not changed, but the new one is different) then install the new one, for it might have new features, bugfixes, etc.
if (original == new) != current (e.g. the default config file has not changed between the original and new packages, but the user has modified their config) then do nothing (to preserve the users settings)
if (original != current) && (current != new) && (original != new)   (e.g. all config files are  different) then create a .pacsave of the current and install the new one
That's all i have to say for tonight.  Maybe tomorrow I'll write something about understanding the startup scripts.

Answer 1

allright... maybe im not done
How to set up the correct timezone
Allright, I like my computer in UTC (even though im in EST/EDT) but some people don't like having to deal with offsets, so here's how to fix it.
1st step:
determine what time your hardware clock is.
easiest method to do this is enter your bios setup and look at the time displayed.  If it's the same as your local time, remember that.  If it isn't figure out if it's UTC from your UTC offset, for instance EST is UTC -500... (EDT is -400... daylight savings).   If that isn't possible, or it's incorrect, just set the clock to your local time.
2nd step:
edit /etc/rc.conf on line 12
this lets the system know how your hardware clock is set up enter "UTC" or "localtime" as per the results of step one
move to line 11
now you choose your timezone
look in /usr/share/zoneinfo/ for your timezone
when setting this i prefer to use the subdir system: e.g. EST/EDT is America/New_York, etc
remember what you finally decided on
3rd step
make a symlink from /etc/localtime to the zonefile you chose in step 2