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It intelligently adds or removes modules.

The kernel log (dmesg)

By counting interrupts generated by an oscillator circuit in your computer. This only functions while the computer is running.

Upon boot-up, the BIOS clock provides a time to the Operating System, at which point they become independent of each other and can differ even if by only milliseconds.

Yes, by the nature of the software they eventually drift. The command hwclock can be used to re-synchronize the system clock and the operating system clock.

No, many server admins choose to use UTC for this reason.

With a number after the device name. For exampe, /dev/hda1, /dev/hda2, etc.

SCSI drives.

Each SCSI device is identified by a unique ID that must be set by a jumper.

No, but you can detect SCSI if the SCSI host adapter has its own BIOS included. Higher end SCSI host adapters generally have this capability, while the lower end ones do not.

Even with a host adapter that includes its own BIOS, you will still need to boot from PATA or SATA drive to detect the SCSI drives.

Yes. SCSI IDs aren’t used to identify the corresponding device file on a Linux system. Hard drives follow the naming system /dev/sdx (where x is a letter from a up), SCSI tapes are named /dev/stx and /dev/nstx (where x is a number from 0 up), and SCSI CD-ROMs and DVD-ROMs are named /dev/scdx (where x is a number from 0 up).

SCSI device numbering (or lettering) is usually assigned in increasing order based on the SCSI ID. If you have one hard disk with a SCSI ID of 2 and another hard disk with a SCSI ID of 4, they will be assigned to /dev/sda and /dev/sdb, respectively. The real danger is if you add a third SCSI drive and give it an ID of 0, 1, or 3.

This new disk will  become /dev/sda (for an ID of 0 or 1) or /dev/sdb (for ID 3), bumping up one or both of the existing disks’ Linux device identifiers. For this reason, it’s usually best to give hard disks the lowest possible SCSI IDs so that you can add future disks using higher IDs.

Yes. Non-SCSI devices such as USB drives or SATA drives can be mapped to the SCSI sub-system, and interfere with the SCSI device numbering if you are not careful.

Devices mid-chain must not be terminated. Both ends of the SCSI chain must be terminated however. A SCSI host adapter qualifies as a device, so if it is at the end of the chain, it can be terminated.

Modern SCSI devices usually include a jumper or other setting to enable or disable termination.

• USB
• IEEE-1394
• SCSI

You configure external SCSI disks just like internal disks, although the physical details of setting the SCSI ID number and termination may differ. This would be described in the manual.

The umount command. Loss of data or corruption of the file system can occur if you simply unplug it.

The x86 partitioning system was extended by a single primary partition as a placeholder for an arbitrary number of additional partitions.

The placeholder partition is known as an extended partition, and all partitions within it are referred to as logical partitions.

Operating systems such as DOS and Windows must boot from a primary partition. Linux does not, and may actually use resources from multiple partitions to facilitate its needs.

The x86 partitioning system uses up to four primary partitions, one of
which can be a placeholder extended partition that contains logical partitions.

One through four.

Examples:

• The third primary partition on the second SCSI disk would be /dev/sdb3
• The first primary partition on the first PATA disk would be /dev/hda1

From five and up, and usually assigned sequentially.

For example, if there is a /dev/hda6, this implies that there is also a /dev/hda5.

The x86 partition table supports partition type codes, which are two-digit hexadecimal numbers that are assigned to specific functions.

Examples:
0x06 is reserved for a certain type of File Allocation Table (FAT) partition.
0x82 denotes a Linux swap partition.
0x83 denotes a Linux file-system partition.

The fdisk command.

Example:
fdisk -l /dev/hdb - This command will show the partition table for the device /dev/hdb.

fdisk -l - this will simply list the partition tables for all devices on the system.

syslogd - otherwise known as the syslog daemon.

The syslogd daemon handles messages from servers and other user-mode programs. It’s usually paired with a daemon called klogd, which is generally installed from the same sysklogd package as syslogd. The klogd daemon manages logging of kernel messages.

For configuration, this is done through the /etc/syslog.conf file. (The rsyslogd configuration file is /etc/rsyslog.conf and is similar to syslog.conf.)

• auth - security/authorization related
• authpriv - privilege related
• cron - cron job related
• daemon - servers/processes that aren't covered by a more specific facilitiy
• kern - kernel related
• lpr -
• mail - used for mail servers and other mail-processing tools
• mark - reserved for internal use
• news - server update/news related
• security - identical to auth, though auth is the preferred facility
• syslog - related to the system logging daemon
• user - user related
• uucp - printing related
• local0 through local7

Asterisk * is a wildcard for all facilities, while the . character can be used to select multiple facilities.

• debug
• notice
• info
• warning - currently used, self-explanatory
• warn - deprecated
• error - deprecated
• err
• crit
• alert
• emerg
• panic - deprecated

Aside from the deprecated codes, the above are listed in escalating importance.

packagename-a.b.c-x.arch.rpm

Packagename - Title of the package, can vary from distributor to distributor

a.b.c - Version of the package. The version number doesn’t have to be three period-separated numbers, but that’s the most common form. The program author assigns the version number.

Build Number - The number following the version number (x) is the build number (also known as the release number). This number represents minor changes made by the package maintainer, not by the program author. These changes may represent altered startup scripts or configuration files, changed file locations, added documentation, or patches appended to the original program to fix bugs or to make the program more compatible with the target Linux distribution. Many distribution maintainers add a letter code to the build number to distinguish their packages from those of others. Note that these numbers are not comparable across package maintainers—George’s build number 5 of a package is not necessarily an improvement on Susan’s build number 4 of the same package.

Architecture - The last part is the package's utilized architecture. i386 is the most common, representing a file compiled for any x86 CPU from 80386 onward. Some packages include optimizations for Pentiums or above (i586 or i686), and non-x86 binary packages use codes for their CPUs, such as ppc for PowerPC CPUs or x86_64 for the x86-64 platform. Scripts, documentation, and other CPU-independent packages generally use the noarch architecture code. The main exception to this rule is source RPMs, which use the src architecture code.