LX0-103 -ALL

Pregunta	Respuesta
Change Logged in User's Password	passwd
Add a user	useradd <username>
Change the password for JoeB	passwd JoeB
Delete user JoeB leaving their home directory intact	userdel JoeB
Delete user JoeB and remove their home directory	userdel -r JoeB
Vi: keystroke to edit/insert	i
vi: exit saving changes	:wq / :wq!
vi: exit without saving changes	:q!
vi: undo an edit	u
vi: save file without closing	:w / :w!
nano: delete whole line	ctrl + k
nano: exit and save or don't save changes	ctrl + x and select option
What information does /etc/passwd contain	bash shell home directory user id user group id username
What file contains information about sudo privileges for users	/etc/sudoers
how do you edit the sudoers file	visudo
how is it best to assign sudo privileges to a user?	add them to a permission group specified in the sudoers file or create a group and add to sudoers
what can be added to the end of sudoers group declaration to bypass need for password to be entered for sudo?	:NOPASSWD:ALL
add existing user JoeB to the group "Wheel"	usermod -G wheel JoeB
What config file determines the default useradd parameters	/etc/default/useradd
create a directory "MyDirectory"	mkdir MyDirectory
how to view the man page for a command	man <command>
what are dot files?	They are hidden configuration files
how can you list dot files in a directory?	ls -a
how to view the last 10 lines of a file	tail <filename>
how to view the first 10 lines of a file	head <filename>
rename file "file" to "file1"	mv file file1
move up 1 level in the directory tree	cd ..
who to get to current user's home directory	cd cd /home/<username> cd ~<username>
how to recursively remove a directory?	rm -r <dir> rm -rf <dir> (if content)
what files are present in /etc	configuration files e.g. bind, ssh, cron etc
what files are present in /var	files that frequently change e.g. log files, library files
How do you redirect output into a file?	> e.g. cat blah.txt > output.txt
What does less do?	Allows navigation of a file
less: move down the file one line	down arrow e
less: move up the file one line	up arrow y
less: move down file one window	f (forward)
less: move up the file one window	b (back)
less: go to specific line e.g. line 20	type in the line number then shift-g
less: search for occurence of word top to bottom	/<word>
less: next occurence of word bottom to top	?<word>
less: when searching for pattern (/ or ?) go to next match	n (next)
what does cron do?	allows user to schedule a task
cron: where are user cron files stored?	/var/spool/cron
cron: how to edit your (user) crontab?	crontab -e
cron: how to edit the system cron?	Edit /etc/crontab (runs as root)
What is YUM?	A RHEL RPM package manager
Yum: search for a package	yum search <package name>
Yum: install a package	yum install <package name>
Yum: download and install system updates	yum update
What is apt-get?	A Debian dkpg package manager
What difference is there between the way YUM and apt-get operate?	apt-get caches repository info on the machine. Everytime you update or search via YUM it goes online to search
apt-get: update the apt-get repo cache	apt-get update
apt-get: search for a package	(sudo) apt-cache search <package name>
apt-get: install a package	(sudo) apt-get install <package name>
apt-get: download and update system packages	apt-get upgrade
top: sort by memory utilisation	shift-m
top: sort by cpu utilisation	shift-p
top: what do the load averages represent?	1min, 5min and 15 min load averages e.g. utilisation of cpu(s) over periods single core: 1.00 is 100% dual core: 2.00 is 100% etc
top: what is the NI column	shows nice values for processess from -20 (highest priority) through 0 (default) to 20 (lowest priority)
top: renice a process	r enter the PID enter nice value
top: kill a process	k enter PID enter sigterm: 15 (quit) or 9 (force quit)
check if locate installed	which locate if not installed use apt-get or yum to install
update locate database	locatedb (as su)
find: search current directory for filename blah.txt	find . -name 'blah.txt'
find search whole system for filenames starting blah	find / -name 'blah*'
apt-get: where would you place a third party repository source	/etc/apt/sources.list
apt-get: how would you clear temporary source files data from the repository	apt-get clean
apt-get: how would you clear temporary repository source files for applications no longer available in the source repository?	apt-get autoclean
apt-get: how would you determine dependencies required for a package?	-s flag (simulate) e.g. apt-get install -s apache2 or apt-cache depends apache2
apt-get: which flag would you use to install a package without user prompting?	-y (yes) e.g. apt-get install -y apache2
apt-get: what flag would omit progress information for an install	-q (quiet) e.g. apt-get install -q apache2
apt-get: how would you download the source files for a package?	apt-get source <package>
apt-get: what is the difference between apt-get upgrade & apt-get dist-upgrade	upgrade installs newest version of installed packages, without removing anything or retrieving new packages. upgrades are ignored if status of another package needs to be changed. upgrade-dist handles changed dependencies.
apt-get: how would you update all packages including those such as the kernel that require changes to dependencies?	apt get dist-upgrade
apt-get: how do you view information about the repository cache such as the number of packages available?	apt-cache stats
apt-get: how do you get a list of all package names, e.g. for grepping and searching?	apt-cache pkgnames
how would you count the number of lines in stdout?	wc -l (wordcount)
apt-get: how do you display unmet dependencies in a repository cache?	apt-cache unmet
How would you display the kernel version of current box?	cat /proc/version or uname -a
what is dpkg?	dpkg is the software that handles .deb package installation, removal etc
dpkg: how would you install a .deb package?	dpkg -i <packagename>
dpkg: how would you install dependencies for a .deb package?	try installing the package with dpkg -i when the install fails with dependences run: apt-get update apt-get -f upgrade run dpkg -i again to install package
apt-get: what does the -f flag do?	-f = fix it attempts fix broken dependencies i.e. where dpkg -i has failed
dpkg: List installed packages	dpkg --get-selections
dpkg: show all files installed with a package	dpkg -L <package name>
dpkg: how would you run a package post-configuration file again	dpkg-reconfigure <package>
dpkg: remove a package leaving configuration files	dpkg --remove <package>
dpkg: remove a package including all configuration files	dpkg --purge <package>
apt-get: what is aptitude?	it is an interface for apt-get that provides a GUI interface on the commandline
what is dselect?	another interface for apt-get
what is RPM	Redhat Package Manager, compiles, installs removes software packages for RHEL based distributions
RPM: install a package	rpm -i <packagename>
RPM: remove a package	rpm -e <packagename>
RPM: what flags show verbose information during an install	-hv (hashes - shows progess bar verbose - displays more info)
RPM: display information about an installed package	rpm -q <package name>
RPM: display detailed information about an installed package	rpm -qi <packagename>
RPM: show all files installed with a package	rpm -q --list <packagename>
RPM: how would you determine dependencies required for a package?	rpm -qR <packagename> (-q - query -R - requirements)
RPM: What does the -U flag do	Upgrade e.g. rpm -Uvh nano.rpm would install the rpm and remove the old version
RPM: what does the -F flag do?	Freshen e.g. rpm -Fvh nano.rpm would only update the package if an existing version of it already exists on the system
RPM: update the rpm database	rpm --rebuilddb
RPM: where is the rpm config file	/usr/lib/rpm/rpmrc
YUM: where is the yum config file	/etc/yum.conf
YUM: where would you add a repository to yum?	/etc/yum.repos.d
YUM: update a specific package	yum check-updates <packagename>
YUM: what is the difference between update and upgrade?	upgrade is the same as update but has the --obsoletes flag set. Better for kernel updates
YUM: remove a package	yum remove httpd.i686
YUM: display information about a package on the repo	yum list <packagename>
YUM: display information about installed package	yum info <packagename>
YUM: show dependencies for an installed package	yum deplist <packagename>
YUM: what flag would force a package installation?	--force
YUM: clean repository, install files etc	yum clean all
what is yumdownloader?	a tool that downloads source RPM packages from yum repositories
how would you download a source rpm file and all of its dependencies?	yumdownloader --resolve <packagename>
what is rpm2cpio	converts an rpm file to a cpio archive
How would you extract an RPM to an archive	rpm2cpio <package> > blah.cpio
list the files in a cpio archive	cpio -t blah.cpio
vi: What are the 3 modes of vi?	command mode ex mode (:) insert mode
vi: Move left and right 1 character	left: h right: l
vi: move up and down 1 character	up: k down: j
vi: move to last line of the screen	shift+l
vi: move to the first line of the screen	shift+h
vi: move to the last line of the file	shift+g
vi: move to a line number	type the line number then shift+g (or gg)
vi: copy a line	yy (yank)
vi: paste copied text	shift+p (line before cursor) p (line after cursor)
vi: undo a change	u
vi: copy a number of lines	type number of lines to copy then yy
vi: search for a pattern	/
vi: delete a number of lines	type number followed by dd
vi: replace word cursor is on	cw
vi: replace line cursor is on	cc
vi: replace text rather than insert	shift+r
vi: search and replace first occurence	:%s/pattern/replacement
vi: search and replace every occurence	:%s/pattern/replacement/g
vi: import content of a file into current file	:r /path/to/file
vi: execute a shell command in vi	:!<command>
what does 'split -l 2 filename' do?	splits filename into two files, using line 2 as the point to split
What are Linux streams?	stdin (input from cmd line) stdout (output displayed in terminal) stderr (error messages)
redirect output to a file	e.g. ls /etc > file
append output to a file	e.g. ls /etc >> file
redirect stderr to a file	<command> 2> file
redirect stdout to a file and stderr to another file	<command> > file 2> errorfile
redirect stderr and stdout to a single file	<command> >file 2>&1
what does the "noclobber" option mean	prevents redirect overwriting a file that already exists
how do you turn on noclobber?	set -o noclobber
grep: how to count matches	-c flag
grep: case insensitive search	-i flag
grep: use a file to input search pattern	-f <filename>
grep: search a directory for a pattern in files	grep -r <pattern> /dir
grep: search directory for pattern in filename	grep -rl <pattern> /dir
grep: what is egrep?	allows extended regexp using \| . * etc
grep: search for a pat1 or pat2	egrep 'pat1\|pat2' <source>
grep: how to return lines not matched	-v
grep: what is fgrep	same as grep -F literal string match, doesn't interpret regex
What does the cut command do?	outputs parts of lines from source, determined by deliminators
how would you output the first field of a line, where the data is separated by colons	cut -f1 -d: <file>
sed: what does sed do?	It is a stream editor, searching and modifying output
sed: find and replace	sed 's/pattern/replacement/' <source>
sed: find and output match to file	sed '/pattern/w output.txt' <source>
sed: prevent standard output	sed <command> >/dev/null
what does the tee command do?	redirects output to stdout and file(s) simultaneously
how would you append output from tee to a file	-a flag
What is the FHS	filesystem hierarchy standard
what does /sys contain?	a virtual filesystem that represents the currently running kernel/system
what does /proc contain?	a virtual filesystem containing information about currently running processes
what does /dev contain	device files
what do /dev/urandom and /dev/random do?	return random bytes based on system noise
what does lsmod do?	lists installed modules from /proc/modules
what does lspci do?	lists pci devices
how would you search for a pci device by slot number	lspci -s <slot number>
what does lsusb do?	lists installed usb devices on the system
how would you view usb devices as a tree diagram	lsusb -t
what is modprobe?	adds and removes modules from the kernel. Older systems (pre centos7) had the -l option to list modules - deprecated in favour of lsmod
how would you remove a module?	modprobe -r <module>
how would you add a module?	modprobe <module>
what does insmod do?	it is an older legacy program that inserts modules into the kernel - requires full path to module file
Grub2: Where is the grub configuration file?	/etc/default/grub
Grub2: what command would you run after updating the grub conf?	update-grub
Grub2: where are the menu options defined?	/etc/grub.d
Grub2: how would you add a new menu option?	Copy an existing entry file and change the number to fit in desired location run update-grub to pull in changes
What file specifies the filesystems mounted at boot?	/etc/fstab
How do you list the UUID's for devices	blkid
What is a cold-plug device?	something that had to be connected/disconnected with power off to prevent system or item damage e.g. cpu, memory, hard-drive etc. Has entry existing in the /dev/ dir
What is a hot-plug device?	One that can be connected/disconnected any time and has built in support or loaded module to function. Entry is created in /dev directory when connected
what information does /proc/mounts contain?	details of mounted filesystems
what virtual filesystem could you cat to get cpu info?	/proc/cpuinfo
What virtual filesystem might you look in to determine system hardware resources?	/proc
what does /bin contain?	essential system binaries required for single user mode e.g. ls, cp etc
what does /lib contain	libraries/shared libraries used by system functions
what does /opt contain	optional application packages you've installed
what does /sbin contain?	essential system binaries e.g. shutdown, init, fsck,iptables etc
What does /usr contain?	"User userble programs and data"
What methods can you use to find boot information?	look in /var/log/messages run dmesg
What is the boot sequence?	System Start (BIOS) Stage 1 Bootloader (MBR - where is loader) Stage 2 - Bootloader (Grub) Kernel (Linux) Init (start user space)
Grub: how would you edit the kernel line parameters?	highlight the kernel option and press e
What do init and telinit do?	Effectively same command, allow you to change runlevel e.g. telinit 1
Cron: What does the cron.deny file do	It prevents users listed in the file from using the cron scheduling system
Cron: what does cron.allow do?	If the file exists, it denies all users access to cron unless they are named in the file explicitly
Cron: do cron.allow and cron.deny need to exist?	No, but if you wish to use them, only one of the other can exist - not both

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