Configuration Files Pertaining to Groups and Users

1. /etc/passwd = contains users accounts and passwords. Entries follow this syntax:

    name:password:UID:GID:GECOS(Text Description of User):homedirectory:shell

    Note: The password field will contain “x” if shadowing is used, and “!!” if no 
              password is set.

2. /etc/shadow = contains shadowed passwords.  This file must be created later if it
    was not created during installation. Entries follow this syntax:

    name:password:lastchange:min:max:warn:disable1:disable2

3. /etc/group = contains groups and their members and GIDs. Entries follow this  
    syntax:     name:password:GID:members  .

4. /etc/login.defs = user account default settings used when adding users.

5. /etc/default/useradd = user account default settings used when adding users.

Configuration Files
vi /etc/motd = Saving text to this file creates a banner “Message Of The Day” that will display
each time a user logs in.  It’s just plain ASCII text.   

/etc/X11/xorg.conf = location of video card driver config file.  You may need to tweak this from
time to time if X Windows will not run the GUI.  If XFree86 is installed, it may also be located in 
/etc/X11/XF86Config .

/etc/fstab = drives to mount automatically

/etc/inittab = daemons to start automatically at certain run levels. /etc/inittab contains the startup
parameters for your Linux installation.  I usually always change the init level from “5” to “3” to boot
up in non-graphical mode and make X Windows optional.  This involves changing the line "initdefault:"
and commenting out the last line in inittab that calls gdm. This has the advantage of freeing up CPU
cycles and memory if I just need the server daemons running and no video/multimedia.

/etc/mtab = contains currently mounted file system.

/etc/hosts = host file of IP to hostname mappings.

/etc/hosts.allow = hosts to allow

/etc/hosts.deny = hosts to deny

/etc/sysconfig/network = hostname

/etc/sysconfig/network-scripts/ifcfg-eth0 -  The IP, MAC and protocol configuration for each NIC.

/etc/ppp/pap-secrets = pap file with ppp connection

/etc/ppp/chap-secrets = chap file with ppp connection

/etc/resolv.conf = client DNS server address settings  (test with “nslookup”) 

Configuring Startup Options
chkconfig = program to add daemons to the Linux startup sequence.  There are three basic switches:

chkconfig –list = display all daemons configured to start at various run levels.
chkconfig –add =  add a daemon to the list to automatically start at a cetain run level.
chkconfig –level = set the init level at which a daemon should start

As an example, we will add all the daemons above to the startup sequence for Linux and have
them all automatically start at init level 3 and init level5:

# NFS Networking
chkconfig –add nfs
chkconfig –level 3 nfs on
chkconfig –level 5 nfs on

chkconfig –add nfslock
chkconfig –level 3 nfslock on
chkconfig –level 5 nfslock on

# SAMBA Networking for Windows
chkconfig –add smb
chkconfig –level 3 smb on
chkconfig –level 5 smb on

# FTP Server
chkconfig –add vsftpd
chkconfig –level 3 vsftpd on
chkconfig –level 5 vsftpd on

# Apache Web Server
chkconfig –add httpd
chkconfig –level 3 httpd on
chkconfig –level 5 httpd on

As an alternative to using the “chkconfig” command, some Linux and Unix systems require that startup
information be added to the “/etc/inittab” file.  This would have the same effect as using “chkconfig”, 
depending on the system and version:

# System initialization.
si::sysinit:/etc/rc.d/rc.sysinit

l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6

# For NFS, restart daemons in this order.
l7:3:wait:/usr/sbin/rpc.mountd
l8:3:wait:/usr/sbin/rpc.nfsd
l9:3:wait:/usr/sbin/rpc.rquotad

# For SAMBA
l10:3:wait:/etc/rc.d/init.d/smb start

# For Apache Web Server
11:3:wait:/etc/rc.d/init.d/httpd start

# For FTP Server
l12:3:wait:/etc/init.d/vsftpd start

Note: Depending on the circumstances and version of Linux, chkconfig or editing
the inittab file may be preferred over other methods. 

Runlevels and “init”

init = also “telinit” used to take Unix/Linux up and down run levels.  In the folders /etc/rc.d/rc0.d to folder
/etc/rc.d/rc6.d are soft links (created with ln –s) that are prefixed with a “K” for killing or an “S” for starting. 
When entering a runlevel, all links with a “K” are killed and all links with an “S” are started. 
The three runlevels to be concerned with are:

1 = single user (diagnostic/safe mode for running fsck and other tools)
3 = full multi user mode, all the daemons but without the GUI or XServer
5 = the full monty, all daemons and the GUI and XServer and a bag of chips!

Environment Files – You can create multiple environment files for different users.
These are usually called “profiles”, and they are executed in the following order:

1.  /etc/profile
2.  ~/.bash_profile
3.  ~/.bash_login
4.  ~/.profile

Note:  Remember that the "~" means the home directory of the current user.
 

GUI Configuration
The GUI of Linux is X Windows.  Remember that in Linux/Unix, everything concerning the GUI is “a la carte”, 
separate from the OS and kernel.  In addition to the commonly used KDE (K Desktop Environment), GNOME
(GNU Object Model Environment) and Xfce desktops, there are many different Window Managers that can be
employed with X Windows.  Some of these are enlightenment (sometimes used by GNOME), fvwm (feeble
virtual window manager), kwin (used by KDE) , metacity (GNOME window manager in Fedora Core 2 - Fedora
Core 4), sawfish, twm (Tab Window Manager), and wmaker (Window Maker).  Configuration files are as follows:

1. /etc/X11/gdm/gdm.conf = configures appearance of gdm (GNOME Display Manager).

2. .Xclients-default = default desktop environment that loads, located in user’s home directory. Remember that
     anything that starts with a “.” Is a hidden file and can only bee seen with “ls –a”.  In thisfile is a line that
     begins with “exec”.  To start a desktop environment by default, change it to “exec” + :

1. gnome-session
2. startkde
3. startxfce4
4. twm

3. .Xclients = points to the .Xclients-default file above.  Located in user’s home directory.

4. /etc/X11/xorg.conf = video card configuration file.  Tweak this with vi if you can’t 
                                     start X Windows.

5. /etc/X11/XF86Config = video configuration file if using XFree86.

Hardware Configuration
1. /proc/cpuinfo – information detected about cpu.
2. /proc/meminfo – information detected about amount of RAM.
3. /proc/dma - information detected about DMA channels.
4. /proc/interrupts - information detected about IRQ assignments.
5. /proc/ioports – information detected about I/O addresses.
6. /proc/modules - information detected about modules installed.
7. /var/log/boot.log = log of services on startup.
8. /var/log/messages = log of messages from system on startup.

dmesg = displays hardware detected by Kudzu at boot time.

The RedHat Package Manager (RPM)
rpm = rpm command.  Syntax:

1. Install a rpm package =  rpm –ivh TheProgram.rpm
2. Query a rpm package = rpm –q TheProgram.rpm
3. List all files in the package = rpm –ql TheProgram.rpm
4. Remove rpm program = rpm –e TheProgram

Note: When running rpm -q APackage to query a package, note that the
         string name of the rpm file in the database is often not the same name
         as the file name, so you must guess a bit. 

Tarballs and Gunzip (compression and decompression)

The older method of installing Unix/Linux programs (in other words, before the most wonderful and
convenient “Redhat Package Manager” - may it live forever), involved using several utilities among
which were those called “tar” and “gunzip”.  Now “gunzip” is easy, it's just “unzip” with a “g”
preceding it, from “GNU”, and sounding like the familiar “winzip” archive utility used by Windows
users.  As far as “tar” is concerned, I'm unsure of the history.  But tar files are called “tar balls” and
effectively they “glue” or “tar” files and directories together into an archive.  When you have spent
all day “tarring” files, you begin to feel rather “tarred”.  Ha ha.  Sorry, just trying to be funny.  Please
don't “tar” and feather me and shoot me with a “gunzip”. Ha ha. Guess I should get
back to explaining things. ( I have no life, this is midnight madness! This is my song.)

A common practice then, is to “tar” a bunch of files and directories to turn them into a single archived
file with the extension “.tar”, and then to “gzip” the tar file to compress the archived file for downloading,
giving it an extension of “.gz”.  This means you must first “gunzip” the file, and then you must “un-tar” it. 
Many times a two step process, and of course there are commands to “tar” and “gzip” things (compression)
just as well as we can “untar” and “gunzip” (decompression) them.

1. gunzip  TheFile.gz = decompresses the file and removes the “.gz” extension.
2. gzip TheFile = compresses the file and adds the “.gz” extension.
3. tar  -xvf  TheFile.tar = extracts “tar ball” archive file.
4. tar -cvf TheFile.tar = creates “tar ball” archive file.

Procedure for Using GCC Compiler to Install Software

1. chmod 777 * - Make all files executable.
1. Type  “./configure”  to run the configure script.  Make any necessary       
    changes before running.
2. Type “make” to compile.
3. Type “make install” to install the file.

Logging In Linux

syslogd = system log daemon
/var/log/* - location of various log files
/etc/syslog.conf = configures log files.  Entries are as such:  
                            Facility.priority   /etc/log/TheLogFile

/etc/logrotate.conf = controls the logrotate settings.

logrotate = backs up and clears log files.

Measuring Performance
mpstat = Stands for “Multi Procesor Statistics”, measures CPU cycles on  Linux Server.  Can specify
the interval in seconds and the number of measurements to make.  Syntax: mpstat 5 7 . 

iostat = disk performace

sar = System Activity Reporter


Printing
Linux uses the Common Unix Printing System (CUPS) for managing print jobs.  It utilizes
“cupsd”, the cups daemon.  Configuration files are located in /etc/cups/cupsd.conf and
/etc/cups/printers.conf.

lp = print a file, the printer daemon.  Syntax = lp –d Ricoh /etc/MyFile.txt

lpstat = display jobs in print queue.  Syntax = lpstat + printer

lpstat –t = list total printers and their status

lp –d = print a print job.  Syntax = lp –d  NameOfPrinter  FileToPrint  .
           Example: lp –d Ricoh1 /etc/hosts

           You can pipe the output of commands to a printer like:
           Example:  ls –la | lp –d Ricoh1 

cancel = cancels a print job in the queue.  Example: cancel PrintJob#
cancel –a = cancel all print jobs

lpadmin = allows you to control/restrict printer access.  Example:

lpadmin –u allow:root,sandrabullock –u deny:all –d Ricoh1 = Allow root and Sandra Bullock
to print to the printer Ricoh1, but no one else.

Configuration of printers can happen several different ways.  You can access it via the GUI
by “RedHat” button -> “System Settings” -> “Printing”.  You may also use:

1. Terminal = system-config-printer-tui
2. GUI = system-config-printer-gui

LPD = Old Unix line printer daemon.  

lpc = views status of printers                Syntax: lpc status
lpr = prints documents                         Syntax: lpr -#2 –P Ricoh1 /etc/hosts
lpq = view status of printer queue
lprm = remove print job from queue     Syntax: lprm 3

accept = enables spooling    Syntax:  accept Ricoh1 
reject = disables spooling    Syntax:  reject Ricoh1
enable = disable printer       Syntax:  enable Ricoh1
disable = enable printer       Syntax:  disable Ricoh1

To cause jobs to be collected in the print queue, one might “accept” printer spooling
for the printer, yet “disable” the printer.

Scheduling
at = schedules an event.  Example: at 9:30pm August 10. After you type at and its arguments,
you will get a prompt.  You may type the commands you wish to execute, hitting enter and going
to the next line for each command.  When you are ready to end, press [ CTRL + d ] to finish.  The
“at” command is for occasional or one time only tasks.  Example:

at 9:30pm August 10
at> ./MyScript
at> ls -l
at> date > TheDate.txt
at> [CTRL + d ]

at –l = display at jobs queued. 
at –d  = remove an at job.  Syntax:  at –d 3 = remove at job 3.
at –c = show contents of at job

/etc/at.allow = Allows users to use at commands.  
                        If not configured, only root is allowed.  
/etc/at.deny = Denies users the use of at commands.

crontab = access cron table.  File located in /etc/crontab and in /etc/cron.d.  The cron daemon is for doing things
repetitively on a cyclical basis.  

crontab –e = calls the vi editor to edit or create the specified crontab text file.

crontab –l = lists cron table

cron tables are structured as follows:

Its just numbers separated by spaces, but the numbers have meaning in their order, 
that is to say in where they are placed.  So, in a crontab file:

13 18 24 8 2 /root/scripts/MyScript  =  Run MyScript at 6:13 pm, August 24 on the 2nd day of the week (Tuesday).    

Quotas
Soft limits = allows user to exceed  quota limits for certain period of time.
Hard limits = rigid, prevent user from exceeding limits period.

1. To enable and configure quotas automatically each time the server boots, you need to add the following entry to /etc/fstab :

LABEL=/        /        ext3        defaults,usrquota,grpquota        1        1

2. Next, remount the root file system using:   mount / -o remount,rw

3. Update the quota database with owned files using:  quotacheck -mavug

4. Turn on quotas on the root file system: quotaon /

5. Edit quotas for different users using:  edquota –u TheUserName .  This command actually just launches the vi
editor and allows you to configure the quota limit text configuration file. Using the command  edquota –u –t  will
allow you to set the time limit for soft quotas. The user quota file has the following structure:
Disk quota for root:

*Note: A “0” for soft and hard means no quota limit for root.

 Disk quota for cgermany:

*Note: 18 Mb soft limit and 20 Mb hard limit for cgermany.  Soft limited to 900 inodes,
           hard limited to 1000 inodes.

repquota = Will produce a report on quotas.  Example:  repquota / 
                 (produces report for root file system)

Backing Up a Unix/Linux System

You system is only as good as its latest complete backup, and after spending all this time configuring things, it would
be nice to back it all up so we don’t have to do it again. 

A. CPIO

cpio = Unix backup utility.  It stands for “Copy In, Copy Out”.  To create a new archive, a list of files must be
created using the “find” or "ls" command.  Then this list can be fed to cpio by using piping procedures.  Works with
all kinds of file systems (not just ext2 and ext3). Example: 

The New Ways: (for the new Linux+ 2004 exam)
ls . | cpio -o >backup.cpio  = backs up files in current directory to "backup.cpio".
find /root/backupfolder | cpio -o > backup2.cpio = backs up everything in /root/backupfolder .
find -mtime 1 | cpio -oav > ~/backup/dev/hdf7/incremental.cpio = find all files modified
with the last day (24 hours) and back them up.

cpio -i <backup.cpio = restore all files from file "backup.cpio"

Zee-old-vays: find /root/Downloads | cpio –vocB –o /dev/hdd2 (no longer works in many versions)
find /root/Downloads | cpio –vocB –o /root/Downloads.cpio

The archive created with by cpio with the above command can be extracted (restored) with the command:    
cpio –vicduB -i /dev/hdd2 .  These files will be extracted recursively to whatever directory you are currently
in when running the cpio command (use “pwd” to see).  To summarize:

1. cpio –vitB –I /root = view a verbose table of contents of an archive
2. find /root/Downloads | cpio –vocB –o /dev/hdd2 = backup to drive
3. find /root/Downloads | cpio –vocB –o /root/Downloads.cpio = backup to file
4. cpio –vicduB -i /dev/hdd2 = extract (restore) backup to current directory

Here's some interesting and useful arguments to use with cpio from the man pages:

B. Dump/Restore

dump – backups to the specified drive and partition (1st argument) and the specified file system
            (2nd argument).  Example:  dump -0uf /dev/hdd1  /dev/hda0  . This would backup the
            boot partition (hda0) to the secondary IDE slave drive on the second partition (hdd1). For partitions
            rather than individual files and directories. 

restore –  Restores backups made with “dump”.  To view the contents of a backup specify its location and use: 
               restore –tf /dev/hdd1 .  To restore the dump above:  restore –vrf /dev/hdd1 .

/etc/dumpdates – file that keeps track of backups for full, incremental, and 
                           differential backups.

Automating Backups

Note that on many versions of Linux you must be in the same directory when initiating a backup job. For this
reason it may be necessary to write a script to change directories and then perform the backup as opposed
to trying to call cpio directly from a crontab file. 

Process and Job Control

ps = Allows viewing running processes which can then be killed. Examples:

ps –f = full option, lists more information per process.
ps –l = lists more information than the –f option.
ps –e = display entire list of processes across all terminals.
ps –a = processes that run across all terminals.
ps -x = processes that do not run across terminals.

*Note: These can all be combined like:  ps –aux and so forth.

kill = stops a running process.  You can specify different arguments with the kills command, or leave them
out and it will use the default kill signal which is 15, or SIGTERM .  Examples:

1. SIGHUP = 1 (Stops and restarts process with same PID.)
2. SIGINT = 2 (weakest, most compatible)
3. SIGQUIT = 3 (core dump)
4. SIGTERM = 15 (default)
5. SIGKILL = 9 (absolute kill)

kill –l = view different kill signal options.

ls /proc/ = lists all processes in subdirectories corresponding to their PIDs.

& = designates a process as a background process to run in the background.  
Example: “MyProgram &” will start MyProgram running in the background.  
The command prompt will return, and the user may do other things while it is running.
Please note that all background job IDs must be prefixed with a “%” character. 
Example: kill -2 %1 . 

jobs = display background job IDs.

fg = moves process to the foreground. Must use “%” to access the PID. Example:
       fg %1

bg = moves process to the background. Must use “%” to access the PID. Example:
        bg %1

nice = sets cpu priority.  A lower nice value increases priority.  A higher nice value decreases it.
The default nice value is 0. The lowest nice value is -20, which would receive the most CPU priority. 
The highest nice value is 19, which would receive the least CPU priority.  Examples:

nice –n 15 ps –aux = would start the ps –aux command with a nice value of 15. 
                                (low priority).
nice –n -20 ps –aux = would start the ps –aux command with a nice value of -20. 
                                 (high priority).

renice = use after a process has been started.  Example:

renice +15 3456 = will reset whatever the nice value is for process 3456 to 15 (low 
                             priority)

©2005 C. Germany