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~/.bash_history

It intelligently adds or removes modules.

The kernel log (dmesg)

Basic Input/Output System

It requires power to remain in use, and is wiped clean upon restart or power loss.

Bootstrapping and/or Booting

The BIOS is stored in non-volatile memory. Traditionally it was stored in ROM (Read-only Memory). EEPROMs (Electrically Erasable Programmable Read Only Memories) was later introduced, introducing the ability to upgrade or update the BIOS using a disk or diskette, without using special tools.

More commonly you will now find Flash memory used to store the BIOS.

POST is performed upon powering on the computer, and stands for Power-On Self-Test.

The bus

PCI is the most commonly used bus type today, replacing the old ISA standard. PCI stands for Peripheral Component Interconnect. ISA stands for Industry Standard Architecture.

The ISA bus was sometimes called the AT bus after the IBM PC-AT in which it was first used in 1984.

ISA supports 8-bit and 16-bit cards.
PCI supports 32-bit devices.

This particular port is called an AGP port, or Accelerated Graphics Port. This port is optimized for the high bandwidth and fast response required for graphics cards.

This is slowly being replaced by the newer PCI Express or PCI-E bus which addresses many limitations of the original PCI design.

The /proc file-system is considered a "pseudo file-system" and contains information about the running system.

Within /proc/pci

A BIOS can now detect when devices or memory have been changed/altered, or even if the case/chassis has been opened or removed.

You can also set a BIOS-level password, though it is rarely used in the business environment.

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.

Cylinders * Heads * Sectors * 512 = Capacity

• ATA stands for Advanced Technology Attachment
• PATA is Parallel ATA - the ATA standard
• SATA is Serial ATA -

SCSI, Small Computer Systems Interface is another common standard, with its own variations.

• ATA stands for Advanced Technology Attachment
• PATA is Parallel ATA - the ATA standard
• SATA is Serial ATA -

SCSI, Small Computer Systems Interface is another common standard, with its own variations.

PATA disks use a parallel interface, meaning several bits are passed through the cable at once.

PATA cables are wide as a result, supporting either 40 or 80 lines, depending on the variety.

They are a bit outdated, but still in use today, particularly in CD-ROM and DVD-ROM drives.

You can connect two devices to each PATA connector. This means that the PATA drive generally has three connectors, as one has to attach to the motherboard.

Each drive should ideally be attached to a separate controller because each controller has a limited throughput. One drive per controller allows for maximum throughput.

They are shown in the file structure as /dev/hda, /dev/hdb, and so on. /dev/hda would be the master on one controller, and /dev/hdb would be the slave on another controller.

For example, if you were to have two master drives, attached to two separate controllers, the numbering scheme would have a gap ending in /dev/hda and /dev/hdc.

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

Serial

Yes, ideally. SATA is capable of 187-375 MB/s, whereas PATA runs at 16-133 MB/s.

SCSI drives.

8 or 16 depending on the variety.

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.

One-dimensionally. Basically, every device in the bus falls upon a straight line.

Each end of the SCSI bus must be terminated - and the bus must not fork or branch in any way. The word terminated refers to a special resistor pack that prevents signals from bouncing back and forth along the SCSI chain. The manual should contain information on how to terminate such a fork or branch.

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.

Four. They are now referred to as the primary partitions.

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.

usbmgr and hotplug

Hot plugging involves plugging in a USB device while the system is running.

The system then has to do the following

• Determine the device, then find a driver to run it
• Bind the driver to the device
• Notify other subsystems about the device. This allows disks to be mounted or print queues to be added for example.

Linux provides LILO, the Linux Loader, which can function as either a master boot program or a secondary boot program. lilo is installed with a command like this one:

# lilo -C /etc/lilo.conf

The -C option specifies the location of LILO's configuration file. (The location in the preceding command is, in fact, the default location, and so the -C clause is redundant.)

The lilo.conf file specifies LILO's behavior for certain aspects of the boot process and also defines the kernels and operating systems that it can boot.

All files in the current directory which are smaller than 12 KByte will be copied to /tmp

grep foo /etc/passwd | cut -d: -f4

A daemon process has no controlling terminal. It cannot open /dev/tty. If you do a "ps -ef" and look at the tty field, all daemons will have a ? for the tty.

The starting of a line, followed by an uppercase letter, followed by a non uppercase letter.

They are removed but you can restore them

quota --report /home

chown foo foobar