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Tables of Contents

Introduction to UNIX

What is UNIX?

• Network Operating System (NOS)
• Multi-tasking
• Multi-user (out of the box)
• Very flexible
• Difficult to learn/use
• Immensely stable

The Long and Winding Road

• Two major flavors (the 1970's)
  • BSD (Berkley Software/Standard Distribution)
  • System V (AT&T/Bell Labs)
• WAR! (late 1980's and early 1990's)
  • Sun teams with AT&T
  • HP, DEC and IBM form OSF
• Two future contenders (2000 and beyond)
  • BSD (FreeBSD, OpenBSD, NetBSD)
  • Linux (Red Hat, Novell, Mandriva, Ubuntu, ...)

Unix Architecture

• Designed to be portable
• Layered design

Introducing Yourself

• UNIX is MULTI-USER!
• User IDs are numeric representations of users defined on the system (e.g. 4005).
• Group IDs are numeric representations of groups defined on the system (e.g. 4005).
• User Names and Group Names are easy to remember mnemonic mappings to User IDs and Group IDs respectively (e.g. fred is user id 4005 and users is group id 4005).

User Authentication

• Traditional Authentication
  • User Name
  • Password
• Other Authentication Mechanisms
  • Kerberos
  • SSH Key
  • .rhosts trust files
  • LDAP
  • Windows Active Directory

Group Authentication

• Every User is associated with a primary default Group.
• When changing current group assignment (if it is possible), some systems may force you to authenticate user a Group password (some UNIX variants do not support this).

Logging In (login)

• Log into an interactive Shell using your User Name and Password.
• You initial login directory under UNIX is called your HOME Directory. Type pwd (Print Working Directory) to see its name.
  

 Welcome to UNIX!

 Login: fred
 Password: ********

 Last login: Wed Aug 26 12:30:05 from console
 $ pwd
 /home/fred

Who's On

• Type id to verify you own an identity.
  • Also can use: whoami, who am i
• Type who to see who is on the system.
  • If available, w -l gives more information than who.

 $ id
 uid=4005(fred) gid=4005(users)
 $ who
 root       tty1       12:00:05
 fred       tty2       14:17:25
 $ whoami
 fred
 $ w -l
 USER    TTY    FROM      LOGIN@    IDLE    JCPU  PCPU  WHAT
 root    tty1   -         12:00pm   5:02    0.09s 0.04s -ksh
 fred    tty2   -         14:17pm   1:03    0.04s 0.02s -ksh

Help Me

• man pages - for commands, functions, formats.
  • apropos - search for a man page.
• info hypertext documentation.
  • pinfo - Lynx-like info replacement.
• Vendor/package specific
  • /usr/share/doc (Linux)
  • WWW search (HTML, PDF, etc.)
• Linux Documentation (sometimes old)
  • http://www.linuxdoc.org

UNIX Fundamentals

• The keys to UNIX are (layman definitions):
  • Processes: Programs which execute with some isolation from one another.
  • Filesystems: A storage area on disk.

Process

• Owned by a User.
• Can receive messages called Signals.
• Termination results in a Return Code.
• Long running ones are called Daemons or Demons.
• Can start other processes called Child Processes or Sub-Processes and thus become a Parent Process.
• The Ancestral Parent of all is the Init Process.

Process Status

• ps - Process Status (System V) (e.g. ps -elf)
  • -e Show all (every) process
  • -f Show all (full) information
  • -l Show more (long) information
  • -u <user> Show user's processes
• ps - Process Status (BSD) (e.g. ps aux)
  • a Show all processes on terminals (tty).
  • u Show user oriented format.
  • x Show processes without a controlling terminal.

Process Status (cont)

• PID - Process ID, a unique number given to a process on a system.
• PPID - Parent Process ID.

 $ ps
 PID  TTY      TIME   CMD
 1012 tty1 00:00:00   -ksh
 1022 tty1 00:00:00   ps
 $ ps -elf
   F S UID     PID  PPID C PRI  NI ADDR SZ WCHAN  STIME TTY ...
 004 S root      1     0 0  69   0 -   109 do_sel 15:58 ?   ...
 002 S root      2     1 0  69   0 -     0 contex 15:58 ?   ...
 ...

The Shell Process

• Common Shells:
  • Bourne Shell (sh) - Always present (sometimes bash).
  • C Shell (csh) - C-like, good for interaction, not for scripting.
  • Korn Shell (ksh) - Excellent interactive and scripting shell with broad availability.
  • Bash Shell (bash) - Excellent interactive and scripting shell popular on Linux systems.
• An easy way to interact with UNIX. Usually the initial process for a login.

Sending Signals to Processes

• Send a signal with kill -<sig#> <PID>
• List all available signals with kill -l.
• You can only signal processes for which you have permissions (own).
• SIGKILL (9) is a SURE kill. Cannot be caught (trapped) or ignored (last resort).
• SIGHUP (1) used to be to respond to communication line hang-ups, but now is used to trigger configuration file changes.

Sending Signals (cont)

• SIGINT (2) is used to interrupt a process.
• SIGSTOP (19) can suspend a running process

Signaling Processes from the Shell

• Control-C (^C) will interrupt (end) the current foreground process, sending a SIGINT to it.
• Control-Z (^Z) will suspend the current foreground process, sending a SIGSTOP to it.
• The command stty -a can be used to see the key sequences associated with the terminal line characteristics intr and susp which send signals to the current shell process when the key sequence is sent from the keyboard.

Process Job Control

• Job control is available in most UNIX shells.
• Job numbers are given to processes:
  • running as a background process.
  • suspended (stopped) after receiving a SIGSTOP (typing ^Z).
• Refer to jobs by job number (e.g. kill %1).
• A job can be changed between background and foreground modes (e.g. fg %1, bg %1).
• The command jobs lists jobs under shell control.

Applying Job Control

 $ man ps
 ...full screen display of man page occurs...
 ^Z
 [1]+ Stopped      man ps
 $ man stty
 ...full screen display of man page occurs...
 ^Z
 [2]+ Stopeed      man stty
 $ jobs
 [1]- Stopped      man ps
 [2]+ Stopped      man stty 
 $ fg %1
 ...full screen display of first stopped man page...
 ...<type q>...
 $ fg %2
 ...<full screen display>...
 ^Z
 [1]+ Stopped      man stty
 $ kill %1
 [4]+ Stopped      man stty
 $
 [4]+ Terminated   man stty

Process Return Codes

• When a process exits it returns a code.
  • 0 = SUCCESS
  • EVERTHING ELSE = FAILURE
• Return code from the last command is stored in a variable called “?”.
• In most shells you can display the contents of this variable typing echo $?.

Examining Return Codes

 $ pwd
 /home/fred
 $ echo $?
 0
 $ pwdirectory
 ksh: pwdirectory: command not found
 $ echo $?
 127
 $ kill %5
 ksh: kill: %5: no such job
 $ echo $?
 1
 $ kill 1
 ksh: kill: 1: Operation not permitted
 $ echo $?
 1

Filesystems

• A way of dealing abstractly with storage.
• Generally uses the concepts of hierarchical directories containing files.
• Does not have to be local hardware.
• Many different types (partial list):

Disks and Filesystems

• Disks are separated into Partitions.
• Partitions contain Filesystems.
• Filesystems contains Directories and Files.
• Filesystems must be Mounted to be used.
• The Root (or /) Filesystem is mandatory and holds special directories called Mount Points where all other filesystems are mounted.
• The root filesystem is implicitly mounted at / (slash) during UNIX boot up.

Disks and Filesystems

Logical Volume Management

• Instead of partitioning, a Logical Volume is an allocation from an available set of storage extents, possibly even across devices.
  • Can migrate data easily.
  • Easy growing of filesystems (e.g. reiserfs) allow you to grow (increase size) while mounted.
  • Avoids the ''running out of slices" problem.
    • Sun and others often call a partition a slice instead.
    • LVM is supported on most UNIX and UNIX-like platforms.

UNIX Devices

• Filesystems are accessed through special files called Device Files located in /dev in UNIX.
  • You mount the filesystem device onto a mount point directory.
  • Filesystem devices are Block oriented devices (move data in chunks) and are usually cached.
• Other hardware also uses special Device Files located in /dev for access.
  • Terminals use Character oriented devices (move data byte-by-byte).

Filesystem Structure

• Logically: Contains files and directories.
• Physically: Just files.
  • Each file is identified by an Inode number (a number guaranteed to be unique within a filesystem). It contains the information about a file including where to get the file's contents.
  • Special files called directories contain a table of names-to-inodes.
  • Filesystem hierarchies are traversed by moving from directory inode to directory inode.
    • The . file entry in a directory is a self reference to that directory inode.
    • The .. file entry in a directory is a reference the parent directory inode.

Filesystem Structure (cont)

Filesystem Operations

• df - Disk Free, shows the mounted filesystems and the available space on each.
• du - Disk Usage, shows space that a directory or files is using.
• mount - (root user) Associates a device (filesystem partition) with a mount point directory.
• umount - (root user) Disassociates a device with its mount point.
• dd - Device-to-device copy.

df

• df -k
  • Disk space in Kilobytes.
• df -H
  • Disk space in readable form (Linux and Solaris 9 or higher).

du

• du [<dir>|<file>]...
  • Total space from this directory downward of all files and directories.
• du -s [<dir>|<files>]...
  • Total space for directory.

mount

• mount <mount-point>
  • Mounts device associated with mount-point in /etc/fstab.
• mount [-t <type>] <device-file> <mount-point>
  • Mounts device-file onto mount-point.
• mount -o <options>,... ...
  • e.g. read only, mount -o ro ...

umount

• umount <mount-point>
  • Disassociates the device with the mount-point. For this to succeed, no one can be using the filesystem.

dd

• dd if=<device-file> of=<device-file> ...
  • Can be used to clone disks with the same physical attributes (cylinders, heads, ...)..
  • Tons of options for handling block size differences.
  • Often used to read foreign tapes, including EBCDIC mainframe tapes.
  • Device-file could be a filesystem file.

Directory and File Operations

• ls - List directory.
• pwd - Print Working Directory
• cd - Change Directory.
• mkdir - Create Directory.
• touch - Create an empty file, or adjust current time stamp of existing file.
• cp - Copy files.
• rm - Remove files and directories.
• rmdir - Remove an empty directory.

Directory and File Operations (cont)

• mv - Move inode directory entry to a different name or different directory.
• cat - Concatenate files. Can also be used to see the contents of a file.

ls

• ls -l
  • long listing, shows permissions, links, size, etc.
• ls -a
  • show hidden files (files that begin with a “.”)
• ls -i
  • show inode numbers.
• ls -F
  • show classification characters.
• ls -t
  • sort by modification time.

cd

• By itself, return you to your HOME directory.
• cd ..
  • go up a directory.
• cd .
  • go nowhere :-)
• cd /
  • go to the root directory.

Pathnames

• Specifying a pathname that does not begin with a / means that the path is relative.
  • usr
  • ../etc
• Paths that start with / can contain relative elements though.
  • /etc/../usr/../etc/passwd

cp

• cp <file1> <file2>
  • Copies <file1> to <file2>
• cp <file1> <file2> <filen>... <dir>
  • Copies <file1>, <file2>, etc. to <dir>
• cp -r <dir1> <dir2>
  • Copies all of <dir1> into <dir2>
• cp -p ...
  • Copy preserving permissions and times (if possible)

rm

• rm <file1> <file2> <filen>...
  • remove files.
• rm -i <file1> <file2> <filen>...
  • prompt before removal
• rm -f <file1> <file2> <filen>...
  • force inspite of permissions
• rm -r <dir1> <dir2> <dirn>...
  • remove recursively all of directory.

Links

• Hard link is the same file inode present in different directories.
• Soft link is a pointer to an inode, the soft link has its own inode.
• ln <file1> <newhard1>
  • Create hard linked file.
• ln -s [<file1>|<dir1>] <newsoft1>
  • Create soft linked file.
• You cannot create your own hard linked directories!

Summary

• UNIX has a HUGE history.
• UNIX can be viewed as processes and files.
• UNIX is truly multi-user.
• Hardware devices are accessed via device files.
• The parent of all filesystems and directories is called the root.
• The parent of all processes is called init.

END DAY ONE