• ls – list dir contents
• ls -al – list all dir contents, in long format.
• ls -F – list contents, dirs noted with / char. BEAUTIFUL!
• mkdir mydir – create dir mydir
• cd dir – change directory to dir
• pwd – print working dir
• mv file1 file2 – move/rename a file from file1 to file2
• tail myfile – read last few lines of myfile
• head myfile – reas first few lines of myfile
• cat myfile – concat files, otherwise displays myfile contents to stout
• rm myfile – removes myfile
• cd .. – cd's one level up(or back) in file structure.
• cd <CR>, cd ~ – quickly cd to home dir
• mv mydir1 mydir2 – moves directories also
• rmdir – remove empty dirs
• rm -r – remove dir recursively (Kills all subdirs)
• touch myfile – creates empty file
• cp -r mydir mydir2 – copies directory recursively (all subdirs)
• services sshd restart – restarted sshd service on X distribution (WHICH ONE?!?!)
• less log.file – page through log.file
  • f key moves forward a page
  • b key moves back
  • / to search
  • ? to search from bottom
  • :20 to goto line 20
  • G & g to goto bottom and top of document
• tee – used in pipes to display stdout as well as output to a file: echo $PATH | tee path.txt
• ls | xargs rm – run rm command on each line outputted from ls. xargs is amazzzing!
• rm $(find ./ -user Christine – rm all files listed from the find command in parens. Amazzzinging!
• expand file – converts tabs to spaces in file file.
• unexpand file – converts spaces to tabs in file.
• od file.txt – display file in octal format. Can display other formats, consult man.
• join file1 file2 – joins lines together based on a key column.
• paste file1 file2 – merge lines in file1 and file2
• sort -k 3 file.txt – Sort file.txt by field 3 (default is 1).
• tr BCJ bc > listing.txt – translate all BCJ chars to bc. -d flag deletes chars entirely in set1.
• sort shakespeare.txt | uniq – uniq removes duplicate lines from shakespeare.txt
• fmt long.txt – format line length and etc in long.txt

• /etc = main config dir
• /var = holds files that freq change (LOGS!)

Files preceeded by a . are hidden/config files and won't show unless -a flag is used in ls cmd.

ls readout: perms, ?, user, group, file, last touched, name.

first perm bit 'd' means it's a dir.

A dot will match any single char except newlines: a.z will match abz aQz a9Z and etc.

A regex may be followed by a special symbol to denote how many times a matching item must exist.

• * = zero or more occurrences
• + = one more more occurrences
• ? = zero or one match

Vertical Bar (|) separates two possible matches:

• car|truck matches either car OR truck.

Surrounds subexpressions (no example in chapter 1)

If you want to match special chars like a dot (.) you must escape it with a backslask: \. (Not unlike bash and python)

Searches for patterns: grep [options] regexp [files]

flags:

• -c # Instead of displaying lines, it displays the count.
• -f # Takes pattern input from a file and not stdin
• -i # Ignore Case
• -r or rgrep # Search recursively.
• -F or –fixed-strings or fgrep # Searches for literal translation, special symbols like $ are now literally printed as $ and not interpreted.
• -E or –extended-regexp or egrep # Uses extended regexp as default

sed 's/2012/2013/' file.txt > new.txt # Change first occurrence of 2012 to 2013 and redirect output to new.txt

• $ ls -la:
  • -rw-r–r– 1 abrer abrer 255 Jan 31 18:37 TeamSpeak3CABDO-ID.ini
  • TYPE OWNER GROUP EVERYONE/WORLD, OWNER, GROUP, SIZE, DATE Moded, TIME moded, NAME

• TYPE bit:
  • - = file
  • d = directory
• Perm #'s:
  • r = 4
  • w = 2
  • x = 1

Can change default permissions with umask.

numeric or symbolic modes.

• numeric = chmod 755
  • 4 = read
  • 2 = write
  • 1 = execute
  • dirs need x to execute

• symbolic = chmod g+x myfile
• chmod u+rwx,g+rwx,o-rw myfile
  • u = user/owner
  • g = group
  • o = other/world/guest

• usermod -g mygroup jeff
  • Sets group mygroup for jeff

• user -a -G mygroup jeff
  • Appends group mygroup to jeff's existing groups.

• chown -R jeff.jeff myfile
• chown -R user:mygroup myfile

: or . works as seperator

Scheduled task system. Stateless, doesn't remember previous jobs.

• cron.deny: Users in this list are denied use of cron
• cron.allow: If this file exists, everyone is denied unless specified here.
• crontab: The schedule file.

Sample Syntax:

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed
*/2 1 1,15 * * root echo "Hello world!" > /tmp/hello.txt # 1st and 15th day of month

# /2 = every 2
# 1,15 = 1st and 15th
# 1-5 = 1st through 5th

Otherwise, symlinking scripts/programs to cron.daily,monthly, weekly, hourly, etc folders will work.

crontab -e to edit user cron, independent from system cron.

• USER CRONS stored in /var/spool/cron
• tail -f /var/log/cron

• rpm/yum - Redhat, Centos, Fedora, Suse
• apt-get/dpkg - Debian, Ubuntu, etc

• Uses yum/rpm.
• Repos listed in /etc/yum.repos.d/

• -ivh packagefile - Installs packagefile with a series of hashes as indicators.
• -uvh - Same as -ive but upgrades a a package if already installed?
• -q pkgname - Queries to see if packagename is installed.
• -e pkgname - remove pkgname from system.

• yum makecache fast - updates local cache of repo contents. Similar to Pacman -Syy
• yum search name - searches repos for pkgs named name
• yum install httpd - installs httpd and deps from repos.
• yum update – updates all packages on system.

uses apt-get / dpkg

Config file located in /etc/apt. sources.list important. sources.list.d folder contains official repos.

• apt-get update – updates repo list. DOES NOT UPGRADE.
• apt-cache search thing – searches packages on local package cache for thing to download from server.
• apt-get install apache2 - install apache2 + deps from repos.
• apt-get upgrade – upgrades out of date packages.

top stuff.

• Sys time, sys uptime, users logged in, load avg (cpu utilization .90 = 90%): 1m, 5m, 15m
• CPU
• Mem
• Swap
• shift M/N? - sort by mem
• shift P - sort by cpu
• NI = nice val. nice vals go from -20 to 19. 19 = LOWEST PRI
• R = renice value - PID - renice val
• K = kill PID [15 = term(inate), kill graceful] [9 = kill, kill forcefully]

Code/functions compiled into files called libraries that other programs/code can call on, reducing code and disk space by not having 50 variations of code that do the same thing.

• Where are libs stored?
  • End in .so extension (prly SHARED OBJECT).
  • Most commonly stored in /usr/lib
    • if on 64bit system, may be stored in /usr/lib64
    • listing files could be libjpeg.so.62 & libjpeg.so.62.1.0
    • Instead of changing name with each revision, new version is installed and the link is updated to point to new library file.

• Library daemon manages most libraries. Called LD.
  • ldconfig -v THIS SHOWS ALL LIBS ON SYSTEM
  • ldd shows lib requirements by program. ldd gimp
  • /etc/ld.so.conf = lib database
  • IF ADDING LIB MANUALLY
    • place lib manually in location like /usr/lib or lib64.
      • Create link to lib.
      • ln TARGET NAMEOFLINK
      • ln ./libdinlibrary.so.5.1.2 ./libdonlibrary.so.5
      • HARD LINKS POINT TO RAW DATA ON DISK
        • (Can only link to data on same partition)
      • SOFT LINKS POINT TO REFERENCE OF DATA ON DISK (File)
        • But moving target breaks the link
      • If adding lib to non conventional location, have to add include statement in /etc/ld.so.conf!

• ps -a list all processes on system
  • First column = PID. 2nd Column = location.
  • ctrl-z background a running process
  • ps alone lists your processes
  • jobs lists running jobs
    • restore by fg job#
    • OR %job#
  • PROGRAM & will background the program and keep it running after you end the shell session.
  • kill PID to end process ID
  • renice # = change niceness of program. 20 = lowest pri, -20 = highest pri.
  • killall -i(interactive) stress (kills all instances of stress
  • pgrep greps ps -A automatically.

• lsmod - list loaded modules
• rmmod - remove module
• modprobe - load a module
• udev maps devices, rules in /etc/udev/rules.d OR /lib/udev/rules.d
• lspci - list pci hardware reported by OS (doesn't mean MODULE is loaded!)
• lsusb - list USB devices

Enumerates hardware before OS is loaded. Drivers will determine how hardware acts in Linux OS. May need to drownload drivers from manufacturers for optimal performance.

drivers loaded in /sys/bus/pci/drivers.

If problems present, check bios. Check drivers! Check lsmod, lspci, lsusb. use modprobe to load modules. Check with the vendor.

Not on exam, but steps demo underlying system that are on exam.

• edit /boot/grub/grub.conf - config file for bootloader.
  • comment out splash image line. (Disables splash image)
  • kernel line, add output to serial: console=tty0 console=ttyS1,9600n8

serial --unit 1 --speed=9600
terminal --timeout 300 console serial

• create new ttyS1 we added in grub.conf.
• vi /etc/securetty
  • add ttyS1 to list on new line.
• vi /etc/init/ttyS1.conf - to edit behavior:
  • start on runlevel [1345]
  • stop on runlevel [S06]
    • lvl1 = single user
    • 3,4,5 = multiuser. 3 = cmd line, 5 = gui 4= ??
    • S = shutdown, 0 = halt
  • respawn
  • instance /dev/ttyS1
  • exec /sbin/agetty ttyS1 9600 vt100-nav -will generate tty interface
  • /etc/inittab shows good info on runlevels. Changing runlevel here will make it default runlevel.

Logicall manages volumes/partitions, create and resize across multiple disks.

• Traditional storage devices look like /dev/sda,b,c,d,etc
• LVM sorts volumes into directories by volume group

• yum install lvm2
• Create the physical volumes
  • pvcreate /dev/sdb /dev/sdc - imports sdb and sdc into lvm.
• Create Volume Group (To hold partitions)
  • vgcreate –help
  • vgcreate vg1 /dev/sdb /dev/sdc - vg1 is name of volume group, change to w/e you want.
• Check your work.
  • pvdisplay
  • vgdisplay
• Create logical volumes (Partitions)
  • lvcreate -L 20G vg1 -n Marketing
    • Reflected in /dev/vg1 (vg1 folder created when volume group created.
    • Need to be formatted and mounted. These are now equiv to devs like /dev/sda1.
  • mkfs -t ext4 /dev/vg1/Marketing
  • can now be mounted
  • Resize LV
    • lvresize -L +2G /dev/vg1/Marketing
      • drive was increased in size. Need to expand filesystem to match.
    • resize2fs /dev/vg1/Marketing - no flags extends to max disk size.
  • Add PVs to volume group.
    • vgextend vg1 /dev/sdd
      • extends volumegroup to device /dev/sdd

Mounts devs on boot.

device      mount     FS     Options -   Dump   - Pass(fschk)
/dev/sda1    /        ext4    defaults    0|1     0|1|2

device = device
mount = mount location
FS = filesystem to expect
Options = boot options (defaults is a combo of options). Like, rw, ro, sync, async, etc.
Dump = old unix backup system. If dump not installed or used, it means nothing. 0 no bkup, 1 = bkup.
Pass = FSCHK, 0 no check, 1 check (high pri), 2 check (2ndary pri)

• Not using GPT, can use lsblk cmd.
  • Awesome cmd! Shows devices, mountpoint.
  • -f shows label and UUID.
• df -h
  • kinda like lsblk.
• blkid
  • shows similar info but for use with GPT.

• tune2fs -L Root /dev/sda3

• whoami - print username
• pwd - print present working directory
• ls - ls contents of dir
• ls -F - puts a slash on directories (handy!)
• tar
  • -c -create tar volume
  • -v -verbose output!
  • -f -filename going to create
  • -z -use gzip on resulting tar file.
  • -x -extract tar.
• cpio
  • find ./file* | cpio -o | gzip > backup.cpio.gz
  • -o = create or –create
• gunzip backup.cpio.gz
  • unzip the cpio gzip archive we made.
• dd for disk duplication/cloning/imaging
  • dd if=/dev/vg1/Sales of=~/sales.img
    • Reverse the order to restore the img.

An alternative init system – (usual is upstart, sysV) Breaks up config files.

Is a program, running all the time. SysV = script, one line/procedural at a time. hangup on one line can cause delays. SystemD, one hung up module won't block all others.

• If /sbin/init = symlink to systemd = systemd
• If /sbin/init = executable = SysV/Upstart

SystemD on boot looks for UNITS and TARGETS.

• unit = various thing on system that can happen at anytime.
• TARGET = groups of units.
  • Calls are units at same time (might be dependencies)

• Config files are in /lib/systemd
  • system dir contains units / targets.
  • .service = a unit
  • httpd.service = a unit.
  • runlevel0.target = symlink, emulates old runlevel behavior.

• httpd.service NOTES:
  • [Unit]
  • Description- Desc of the file
  • After=network.target remote-fs.target – don't run httpd.service until AFTER these targets are started.
  • Wants=samedepends – means if one arg here stopped running, httpd.service will continue to run.
  • [Service]
  • Type=notify - lets us know if it worked, didn't work.
  • Environment=?? no idea
  • ExecStart=/usr/sbin/httpd $OPTIONS -DFOREFROUND (this is how it's started, AKA systemctm start httpd.service)
  • ExecReload=/usr/sbin/httpd $OPTIONS -k graceful
  • ExecStop=/bin/kill -WINCH ${MAINPID}

• Control systemd by:
  • systemctl start httpd
  • systemctl stop httpd
  • service httpd start now redirects to systemd

• in /usr/lib/systemd/system dir:
  • default.target = symlink to graphical
    • Sets defaults of system (like runlevels)
    • can change default.target link to cmdline instead of graphical for terminal boot.

• Xorg -configure – Runs xorg config to generate generic xorg conf to get X running again!

Both used to search for files. locate uses a database of information to search and is updated via a syscron or manual updatedb. find will search the disk in specified locations for files and objects.

• locate motd
  • searches for motd.
  • may not be installed by default: apt-get install locate, yum install mlocate
• find /etc -name motd
  • search in /etc for files containing motd.