Linux (Debian)
Distros● Debian GNU/Linux
● Debian based: Ubuntu, Knoppix, Linspire, Damn Small Linux, etc. ● Red Hat, Slackware, SUSE, Mandriva, CentOS, Gentoo, etc.
● “Linux” is just the kernel, it's what allows the system to boot up and talk with your
machine's hardware.
● GNU (Recursive acronym: “GNU's Not Unix”) was a project launched in 1984 to
develop a complete Unix-line operating system which is free software. The GNU project was never able to develop a kernel, so that started using the Linux kernel to run all of their software on.
● Free Software? liberty, not necessarily price. Think of it as “free speech”, not as in
“free beer”. Although, most open source software is free in both ways.
● Common items in “Linux”: Shell (text terminal/console), a graphical environment
know has the “X Window System”, sometimes referred to as “X11”. GNOME or KDE desktop environment.
● Bar at the left/right/top/bottom is called the “Panel” (similar to taskbar in Windows
).
● Terminal Windows (console/shell window). Similar to Windows Command Prompt. ● Common partitions/directories: /, /home, /usr, /var, /tmp, swap
● Directory paths use forward slash “/” in Linux. (Backslash “\” in Windows)
Hard Drives & File Systems
● Managing your Hard drives in Linux:
○ Gnome System Menu -> Administration -> Partition Manager: Allows you to see
how your hard drive's partitions and the types of file systems that your partitions are using.
○ Shell tools: fsck for checking hard drive for errors. cfdisk for partitioning drives.
mkfs.ext3, mkfs.vfat, etc. to format the partition with a specific file system.
○ Partitions are usually mounted to directory mount points. “df” command will
show you which partitions are mounted to which directories.
○ Mounting/Unmounted file systems (partitions) in linux:
mount -t ext4 /dev/sda4 /mnt umount /mnt
You can also use mount/umount to connect/disconnect network shares (like nfs shares):
mount -t nfs 192.168.1.123:/share1 /mnt umount /mnt
○ File systems are usually mounted at boot time via the /etc/fstab file. ○ In Linux you need to have at least 2 partitions: / and swap.
● File Systems:
○ ext (extended file system): The first file system ever created for linux.
○ ext3 (third extended file system): 3rd generation of the ext file system that now
supports journaling along with a number of other improvements to the file system. ext2 and ext3 used to be the most common file systems used in linux, but now replaced by ext4. ext3 supports up to 16TB file systems, and 2TB file sizes.
○ ext4 (fourth extended file system): 4th generation of the ext file system which
now upports up to 1EB file systems and 16TB file sizes. ext4 is also faster then all previous ext versions and has support for SSD drives via TRIM.
● Advanced File System Features:
○ Logical Volumes: Extending file systems (partitions) across multiple disks to
create larger volumes and make it easier to expand in the future.
○ Software & Hardware RAID - Redundant Array of Independent Disks
(Inexpensive Drives).
Bootup/Shutdown
● During the Linux install, some code is written to your hard drive's MBR (Master
Boot Record) which tells your computer what files to load from your hard drive to load Linux. This program is usually either LILO (Linux Loader) or GRUB (GRand Unified Bootloader). With most linux boot loaders, you are presented with a boot screen that allows you to choose which kernel to boot.
● Runtime levels (init levels): ○ 0: shutdown
○ 1: single user mode ○ 2: normal user mode ○ 6: reboot
For instance, this command will cause your system to reboot: /sbin/init 6
And this command will cause your system to shutdown: /sbin/init 0
● Other command to shutdown and reboot your system:
shutdown, halt, reboot
● Single User Mode allows you to troubleshoot your system and perform
hardware/software maintenance. Similar to Windows Safe Mode.
● When was the machine last booted? From a Shell/Terminal run: uptime
● Locking Screen or Logging off: Gnome System Menu -> “Lock Screen” or “Log Out” ● Startup Scripts: /etc/rc#.d/* (# is 0, 1, 2, or 6) These scripts get run when
entering or exiting a specific runtime level. Scripts will either start with an S (start) or K (kill), followed by a number to specify an order in which the scripts should run, for instance: /etc/rc2.d/S10syslog-ng, /etc/rc2.d/S89cron
Account Management
● Creating and managing user accounts via Gnome System Menu -> Administration
-> Users and Groups. Allows you to add, delete and change user accounts.
● Shell/Terminal:
useradd -m -g users -u 1001 -s /bin/tcsh -d /home/joe joe userdel -r joe
● /etc/passwd, /etc/shadow, /etc/group
○ /etc/passwd contains account information:
7 fields: username:x:uid:gid:Account Name:home dir:shell uid = user id number, integer | gid = group id number
○ /etc/shadow contains account password and other password settings:
9 fields: username:password:?:?:?:?:?:?:?
○ /etc/group contains group information:
4 fields: groupname:password:gid:list of users for this group
password is usually not used (usually an “x”), and the list of users is comma separated like: video:x:44:demo,tom,mike
● New Account config files are stored in /etc/skel, they get copied over to the user's
home directory (/home/username) when the account gets created.
● Groups: Users can be in multiple groups so that they can do specific things on the
system. For instance, in order to be access your computer's cdrom drive, you must be part of the “cdrom” group. Or for printing, “lpadmin” group.
● NIS (Network Information Services) aka YP (Yellow Pages): A client-server directory
service protocol that allows you to share accounts between a server and clients.
Quotas
● Enabling Quotas:
Edit /etc/fstab and add the options “usrquota,grpquota” to any partition you want quotas enabled on. Reboot, then run: quotacheck -F vfsv0 -v -c /home
● Commands to control quotas:
edquota: to setup (edit) a user's quota
quota -v: To view a user's quota (they can only view their own) root can view all users' quota: quota -v username
File Permissions
● Changing ownership and permissions on files and directories: Right-click on file or
directory and choose “Properties”. Under the “Permissions” tab, you have the ability to set the different permissions for owner/group/other.
● 4 different types of permissions: read, write, execute, and none for
owner/group/other. The “chmod” command allows you to set the permissions on files. The “chown” command allows you to change ownership of files (when root). Sample file permissions:
rwxr-x--- root sys file1
read/write/execute for “root”, read/execute for group “sys”, none for other.
Linux Memory Management
● RAM and Swap space. A swap file (virtual memory) is simply a file that linux will
use in place of memory if it runs out of physical memory.
● Under the Gnome Application Menu -> System Tools -> System Monitor,
“Resources” tab, allows you to see your physical and swap memory usage.
● Shell/Terminal: “free” command shows physical and swap memory usage.
Networking
● Gnome System Menu -> Administration -> Network. Highlight the “Wired”
interface and click “Properties...” So long as “Roaming mode” isn't selected, then you'll see that it's very similar to Windows, you can either use DHCP or manual (static info) for your network settings. If you Cancel out of that interface's properties, then you'll see the following tabs: Connections, General, DNS, Hosts.
● Shell/Terminal: ifconfig, hostname, netstat, ping ● Config files: /etc/network/interfaces (for Debian)
Process/Job Management
● Under the Gnome Application Menu -> System Tools -> System Monitor, “Process
Table” tab, allows you to see what processes are running your system system and kill them, “End Process”, if necessary. Allows you to see who is running the
process, how much CPU resources or Memory a particular process is using, along with the process's PID (process ID #).
● Shell/Terminal:
ps -aef | more [list process] kill pid [kill process]
kill -9 pid [forcefully kill process] top [interative process monitor]
Job Scheduling
● cron configuration files:
/etc/crontab sample entry: 0 1 * * 1-3 root /command/to/run
7 fields: minute, hour, day of month, month, day of week, user, command
Config Files
● Most configuration files in linux are plain text files. Files like /etc/hostname,
/etc/passwd, /etc/shadow, /etc/fstab, /etc/crontab, etc, .etc.
● A lot of user configuration files in a user's home directory (/home/username or
~/username) are “dot” files like “.cshrc”, “.bashrc”, “.profile”.
● A large number of front end applications to edit config files (GUI based, text based,
and web based).
Daemons
● Programs that run in the background to perform some special function (SSH server,
Remote Desktop, DNS server, DHCP server, event logging, etc.)
● Gnome System Menu -> Administration -> Services: Start, stop and disable
services from here.
● 3 ways to startup jobs/daemons:
1. startup at bootup (vi /etc/rc scripts)
2. via cron, schedule job to run/startup at a specific time.
3. via inetd daemon: Startup daemons as needed. inetd daemon will run at all times, and will startup daemons (from /etc/inetd.conf) when needed.
● You can see what processes are running via shell/terminal:
ps -aef | more
Logs
● System logs are logged via syslog-ng (or older syslog) daemon. Logs are normally
stored in /var/log directory under different service name files.
● You can also see what your kernel is doing by running: dmesg
● Common log files: /var/log/syslog, /var/log/mail.log, /var/log/auth.log, etc.
GUI vs TEXT
● Graphical: Point & Click. Large number of possible graphical environments: Xorg,
Xfree86, Xgl are the X Window Systems. GNOME & KDE are the common desktop environments. Then you have the window managers: metacity, Compiz Fusion, etc. etc. Very customizable...
● Shell/Terminal: Easily write scripts to automate tasks. Easy to do remote
administration via SSH.
Shell Commands
● Number of different shells available: sh, csh, tcsh, bash, zsh, etc... ● Get help with “man cmd”
● Some general commands: cd, ls, mkdir, rmdir, rm, mv, cp, cat, more, echo
Updates
● Linux update-manager for Debian takes care of updates (similar to Windows
update manager).
● Shell/Terminal: apt-get update; apt-get upgrade
● Upgrading the system's kernel is usually the only time Linux ever needs to be
rebooted, and even that now-a-days can sometimes be done without rebooting your system. (Compared to Windows, which requires a reboot with most updates).
Package Management
● Gnome System Menu -> Administration -> Synaptic Package Managerallows you to
install and uninstall programs.
● Debian Linux Packages: DEB packages ● Red Hat Packages: RPM packages ● Debian Package installation:
○ apt-get install package-name ○ dpkg -i package-name.deb
○ aptitude is a text based shell package manager. ● Compiling and installing software from source:
tar xf package-name.tar ./configure
make
make install
Backups & File Compression
● The “tar” command is the easiest to use to archive a number of files into one file
which you can then compress (with gzip or bzip2):
tar cfp /tmp/new_file.tar /etc/hosts /etc/hostname [compress] tar xfp /tmp/new_file.tar [extract]
● Most commonly used file compression formats are gzip and bzip2 in linux:
gzip /tmp/new_file.tar [gives you a new_file.tar.gz file] gunzip /tmp/new_file.tar.gz [gives us new_file.tar]
bzip2 /tmp/new_file.tar [gives us new_file.tar.bz2] bunzip2 /tmp/new_file.tar.bz2 [gives us new_file.tar]
● dump/restore: Common unix/linux command for dumping files or entire partition to
some backup area and restoring them as needed.
● Backup to tape, CD, DVD, or disk-to-disk (external USB drive, or NAS/SAN)
Programming
● A large number of programming languages available for Linux: C, Java, Python,
Perl, Shell scripts, etc.
File Sharing
● Linux uses NFS (Network File System) was back in 1984 as a way for Unix systems
to share their file systems between different machines.
● On the server export a directory via NFS by editing /etc/exports and adding an
entry like so:
/home/share1 192.168.1.101(rw,sync,no_root_squash,subtree_check) /home/share2 *(ro,sync,no_root_squash,subtree_check)
● On the client, you use the mount command to access the share like so:
mount -t nfs 192.168.1.100:/home/share1 /mnt [mount share] umount /mnt [unmount share]
● Access Window shares via Samba, you can mount a Windows share via:
mount -t smbfs username=username,password //server/share_name /mnt (You will be prompted to type in a password)
Remote Management
● VNC (Virtual Network Computing): Remote Desktop protocol that is cross-platform,
supported on: Windows, FreeBSD, MAC, Unix/Linux, etc.
● SSH (Secure SHell) access to shell/terminal from a remote location. Very secure,
powerful and fast. Uses very little network bandwidth.
Security
● File/Directory ownership/permissions ● Linux software firewall (iptables)
● Hardware Firewall for better protection
● Anti-Virus (Clamav): To protect other Windows system on network. ● Disable unneeded services (telnet, etc.)
Miscellaneous
● Web: Apache Web Server ● Email: Postfix Email Server
