View difference between Paste ID: Z4jy6dvv and EwnGpsby

 Interrupt the Boot Process in Order to Gain Access to a System
 To start the system in the Rescue target, during boot process edit the grub config kernel line by adding to the end: systemd.unit=rescue.target
 1. During boot process, edit grub config kernel line “linux16” by adding to the end: rd.break
 2. mount –o remount,rw /sysroot
 3. chroot /sysroot
 4. passwd
 5. touch /.autorelabel
 6. exit then exit again
 
 REDIRECTION
 &> == Redirect both
 2>&1 == Redirect standard error to output
 
 UMASK
 Default: 666 files / 777 directories
 Permanent adjust for users: /etc/profile and /etc/bashrc
 
 SHUTDOWN/REBOOT
 shutdown [flags/arguments]
 	-r == reboot
 	-h / P == halt / power-off
 	+# / 00:00 == in minutes / military time
 systemctl [halt/poweroff/reboot]
 
 PERMISSIONS
 chmod
 	g+s [directory] // chmod 2xxx == all files/dir created inside will be created 				with the group ownership of this directory
 	u+s [file] // chmod 4xxx [file] == execute as owner of file
 	1xxx [directory] == files/dir inside cannot be deleted except by owner of that 				file/dir
 	capital letter == apply only to directories
 
 NICE
 19 (least) to -20 (most)
 nice
 	–n # [name] == start process with specific process, the -n IS required
 renice
 	–n # [pid] == renice a specific process by id
 	-n # $(pgrep [name]) == renice every process found by pgrep ($ creates a subshell)
 
 
 PROCESSES
 pgrep [flag] [name] == shows process id and name
 	-l == list process name
 	-u [username] == find only those owned by [username]
 	-v == inverse results (Ex: pgrep –v –u root == all processes not owned by 		root)
 	-t [pts/#] == kill all process started by that user/terminal window, but user 			stays logged in
 
 SIGHUP/1 == Closing terminal
 SIGINT/2 == Keyboard interrupt (ctrl + c)
 SIGQUI/3 == Parent process tells it to quit
 SIGKILL/9 == Murder the process. Do not pass go.
 SIGTERM/15 == Stop, cleanup, and quit. DEFAULT used when kill/pkill
 SIGCONT/18 == Continue
 SIGSTOP/19 == Stop
 kill [pid] == kill a specific process
 pkill [name] == kill all processes of that name
 ps axo nice,comm,pid,user
 
 LOAD
 0.00 , 0.00, 0.00 == 1 minute, 5 minutes, 15 minutes
 0.00 (min) / # of processors == % of cpu usage
 	1 cpus w/ 1.00 == 100% cpu power
 	2 cpus w/ 1.50 == ~75% cpu power
 
 
 USERS/GROUPS
 useradd // usermod // userdel // chage
 groupadd // groupmod // groupdel
 newgrp == change my current group ID during this login session
 /etc/passwd == username: x: user id: group id: nickname: home dir: login
 /etc/shadow == username: pw hash: last pw change unix epoc: min days before pw change: max days before required pw change: # of days of warning before pw expire: max active days after pw expire: account expiration date
 /etc/skel == skeleton user directory
 user login defaults == /etc/login.defs
 Other defaults == /etc/defaults/
 
 TAR/GZIP
 **Extracting by default overwrites local files**
 tar -cvzf NAME.tar.gz [files/directories]
 	-c == create
 	-v == verbose
 	-z == gzip
 	-x == gunzip
 	-f == name the file
 	-t = look inside without unpacking
 	-d == see difference between local and archived
 
 TRANSFERING FILES
 scp /path/to/local/file user@remotehost:/path/to/destination
 sftp user@remotehost
 	-can use basic CLI commands such as ls and mkdir
 	-“get” == download file from remote
 	-“put” == upload file to remote
 	-“?” == help/commands
 To Push:
 rsync -a /path/to/file_or_dir user@remotehost:/path/to/destination
 To Pull:
 rsync -a user@remotehost:/path/to/remote/dir_or_file /path/to/local/destination
 	-a == stands for "archive" and syncs recursively and preserves symbolic 		links, special and device files, modification times, group, owner, and 		permissions
 	-nv == verbose dry run
 	-z == compress first
 	-P == combines progress and partial flag, gives a progress bar for the 			transfers and allows you to resume interrupted transfers
 	--exclude=/what/to/exclude
 By default, rsync does not delete anything from the destination directory, but can change this behavior with the --delete option
 AT, CRON,  ANACRON
 AT does not create reoccurring events, only a one time scheduled future event.
 If system is off during cron time, cron is missed.
 Anacron checks last time cron was run.
 yum install at
 (then make sure to enable & start the service)
 at.deny OR at.allow
 
 at
 	now +## [minutes/hours/days]
 		>[command] then ctrl+d
 	at [time am/pm]
 		>[command] then ctrl+d
 
 atq == list at queue
 atrm # == remove job
 -------------------------
 cron.d == custom crons / crons that are managed by a program
 –---------------------------
 anacron == only privileged users
 /var/spool/anacron/ == logs kept by anacron for last run cycle of a cron
 anacron -f == Run all anacronjobs regardless of their last run timestamp
 
 TARGETS/SERVICES
 /usr/lib/systemd/system/ == location of services, targets, etc
 systemctl
 	is-enabled [service] == check if service is enabled on boot
 	is-active [service] == is the service active/on right now
 	enable/disable [service] == enable/disable service to start on boot
 	--type=target == list all active targets
 	--type=service == list all active services
 	set-default == set default runlevel at boot
 	get-default == what is the default target to run at boot?
 	-t help == list all available system config units
 	list-dependencies [target]/[service] == list all dependencies (if no [target]/	[service] specified, then the dependencies of target you are in now are listed)
 
 /etc/systemd/system/[target_name].target.wants/[name].service == enabled services. Symlink from here to /usr/lib/systemd/system/[service] is created to enable
 
 
 systemctl XXXXX name.target
 	isolate == Move from one target to another (i.e. from multi-user to graphical 	interface to rescue mode, etc.)
 
 
 ACLs (Access Control Lists)
 default working filesystems= xfs. Ext works too but must be specified when mounted
 Gives user access to specific file/dir without making them part of the group or the owner. Adds a + to permissions to show this for users/groups but not world.
 getfacl == get ACL info
 	Can use to copy ACL info:
 		getfacl file1 | setfacl --set-file=- file2
 		(note the - after the =, this implies coming from std input)
 	>mask == maximum level permissions; overrides specific ACL; modified by chmod.
 setfacl [flags+arguments] file/dir
 	-m == modify
 	u (notice no -) == user, used this way == u:username:permissions
 	g (notice no -) == group, see “u” flag for usage
 >Note: u and g map to the UID/GID respectively, so if either one is changed for a user/group, ACL will no longer apply to that user/group!
 	m (notice no -) == mask. Used this way == m::permissions
 	-d == set defaults for user inside directory (goes before -m)
 Default ACL on directory == all files/dir created under will have this ACL, but the user still needs to have their own ACL permission on the directory
 In other words, ACL affects how the directory can be used (read, write, execute), and default ACL affects the files/dirs the user makes inside
 	-x == remove ACL for user/group
 	--remove-default == removes all defaults
 	-R == recursive
 You can combine, ex:
 	setfacl -m g:mygroup:rwx,u:myuser:rw directory
 cp doesn’t preserve ACL rules
 mv does preserve ACL rules
 
 Configure a System to Use an Existing Authentication Service
 yum upgrade –y
 yum install –y realmd
 realm discover [hostname]
 yum install –y [required packages]
 realm join [hostname]
 vim /etc/ssh/sshd_config == uncomment + allow authentication (kerberos?)
 systemctl sshd restart
 
 LOGS/JOURNALD
 journalctl == systemd logs everything here (man systemd-journald). It is not 			persistent, it clears out after every reboot.
 
 	--since=yesterday == all logs since that day (only if persistent or hasn’t been 					rebooted)
 
 /etc/system/journald.conf == journald config file
 /etc/rsyslog.conf
 	mail.* == “mail” is a facility, the type of program creating log
 	*.emerg == “emerg” is priority. Info, debug, warning, etc.
 systemd-analyze == boot times
 systemd-analyze blame == specific times for boot processes
 
 VIRTUAL MACHINES
 To install VM packages:
 yum grouplist hidden (This will show virtualization packages)
 yum groupinstall "Virtualization Client" "Virtualization Tools" "Virtualization Platform"
 
 systemctl enable libvirtd
 systemctl start libvirtd
 
 virsh == CLI virtual machine manager
 	help
 	list --all
 	shutdown [vmname]
 	start [vmname]
 	autostart [vm-name]
 virt-manager == GUI virtual machine manager (applications > system tools 			> virtual machine manager)
 
 FIREWALLD
 yum install firewalld firewall-config
 
 firewall-cmd [options]…
 --help == help/info
 --get-zones == shows you the zones available. all rules are saved in “zones”
 --get-default-zone == youre always working in a zone, this shows you the default one a rule is applied to unless you specify a zone
 
 
 --list-all == list all current rules for the default zone, unless you specify the zone:
 --zone=[zone] -- list-all
 --list-all-zones == list all current rules for all zones
 
 --reload == reload firewalld
 --permanent == make rule permanent. Permanent rules are not applied until you reload
 
 --add-port=[port #]/[tcp or udp] == add port with either tcp or udp
 --add-source=[IP] == add source IP
 --remove-port=[port #]/[tcp/udp] == remove port #
 --remove-source=[IP] == remove source IP
 
 SELINUX
 Modes:
 	Enabled == monitoring + enforcing
 	Passive == monitoring + logging but not enforcing
 	Disabled == Not monitoring or logging or enforcing (reboot required to go 			into disabled mode)
 getenforce == what mode are we in?
 setenforce 0 == change to Passive/Permissive mode (if its not the default, it will 			revert on reboot)
 setenforce 1 == change to Enabled/Enforcing mode (if its not the default, it will 			revert on reboot)
 /etc/selinux/config == Change default level, and ability to Disable (must reboot to 				apply disable)
 ls –Z == list SELinux info
 	-rw-r--r--. root root unconfined_u:object_r:admin_home_t:s0 file.out
 	Permissions / user:group / user / role / type / filename
 	type = specific program or permissions allowed to access
 semanage fcontext -l | grep [process/file/directory] == list all files/dirs associated with [ ] 									in SELinux
 restorecon [file/dir] == “restore” context of [ ] based on where it currently is located
 touch /.autorelabel == force relabel everything on reboot
 semanage fcontext -a -t [context] '[file/path]'
 	-a (add) -t (type) : add a file/path to SELinux context rules.
 	For example, adding a path with optional recursive to all files/dirs to the main httpd 	context rule:
 	semanage fcontext -a -t httpd_sys_content_t '/content(/.*)?'
 semanage fcontext -d "[file/path]" == -d (remove) : remove SELinux rule. Must restorecon in 						that directory or the file to apply
 getsebool -a == list SELinux boolean values currently set
 semanage boolean -l == list SELinux boolean default values
 setsebool [-P] [bolean_rule] on/off == change Boolean rule. By default its for this session only, 						but if you set [-P] then it because permanent.
 yum install setroubleshoot-server == not pre-installed by default. Creates 									/var/log/audit/audit.log but not user friendly so use: 						sealert -a /var/log/audit/audit.log
 
 
 Key-Based Authentication for SSH
 ssh-keygen == generate RSA private and public keys
 ssh-copy-id [user]@[IP] == copy the public key (id_rsa.pub) to a remote machine
 
 ssh-agent bash && ssh-add == cache ssh passphrase for this session
 
 MANAGING NETWORK
 nmcli con show == show connected network devices
 nmcli dev status == like above, but cleaner + state
 nmtui == connection editor wizard
 
 nmcli con [add/del] [use tab for options] == add/delete connections
 nmcli con [up/down] “[connection name]” == bring up/down connection
 nmcli con mod “[connection name]” (use tab-tab to search) == modify connection
 	+ipv4.dns [IP] == add DNS resolver to specific connection
 
 
 /etc/sysconfig/network-scripts/ == network and device scripts
 
 ip addr == show connections
 	show [device] == optional for seeing info one only specific device
 	-s  [what] show [device] == stats of device
 ss == see listening ports + established connections
 	-a == all listening/established
 	-t / u == tcp / udp
 	-n == include port. External on left, internal on right.
 hostname [hostname] temporary hostname change
 vi /etc/hostname == permanent hostname change
 
 KERNEL
 yum list kernel == list available/installed kernels
 grub2-set-default [#] == change kernel used to boot
 	# == 0 most recent, 1 older, 2 even older, etc
 yum update kernel == update kernel
 yumdownloader kernel == download kernel rpm
 rpm -ivh kernel..[tab] == install new kernel (reboot to take effect)
 
 INSTALL REDHAT w/ KICKSTART
 A Kickstart file automatically gets created by the  anaconda installer at the end of a RHEL installation. It is saved at the root user s home directory, and has the name /root/anaconda-ks.cfg
 
 yum install system-config-kickstart == install kickstart config tool, use same name 						to start tool
 TAB at boot install, ks=[http/ftp]://path/to/file
 
 TIME SERVICES
 chronyd == what ntp uses as a daemon, instead of ntp.d
 timedatectl == time/date services
 	set-timezone [America/Los_Angeles]
 	set-time [hour:minute:second]
 
 tzselect = timezone selection assistance (does not actually set it for you)
 chronyc
 	sources -v == show ntp servers
 	tracking == verbose info on synchronization
 /etc/chrony.conf == chrony config, pool of servers being used for sync
 
 
 INSTALL/UPDATE/MANAGE PACKAGES/REPOS
 yum == yellow-dog updater modified
 yum
 	check-update == list updates only, don't attempt to install
 	info == info of package
 	list installed [package] == check if specific packaged installed, not a result of 				everything named [package]
 	provides/whatprovides [path/file] == what created this file/directory
 yumdownloader == download package
 -----------------------------
 rpm -[flag below] [package]
 	-i == install
 	-e == erase
 	-vh == verbose + progress bar
 	-U == update package
 	-qa == check if package installed
 	-ql  == list files installed
 	-c == config files
 	-d == documentation files
 rpm localinstall [package] == install using yum
 --------------------------------------
 yum repolist all == list all enabled and disabled repos
 yum-config-manager
 	add-repo [url] == add repo file
 	--disabled [repo ID from yum repolist all]
 ------------------------------------------
 Repo files must end in .repo :
 [repo id]
 name=name of my repo
 baseurl=file:///path/to/directory OR https://url.domain.com
 enabled=1
 gpgcheck=0
 OR
 gpgcheck=1
 gpgkey=file:///etc/pki/rpm-gpg/GPGKEYURL
 gpg keys location = /etc/pki/rpm-gpg/  (use wget to dowload)
 
 STORAGE
 fdisk /path/to/mount == mbr partitions only
 	For “last sector” (i.e. size of partition), you can do +#M/G . Example: +500M 		is 500 MB, +25G is 25GB
 	Don't forget to hit ‘w’ to write changes!
 mkfs [flag and option] /path/to/partition
 	-t [type] == specify type of filesystem, red hat defaults as xfs
 blkid == see device info
 >Need to create location to mount device, generally done in /mnt/
 mount -U [UUID] ← this method is preferred but can also do mount [device path] 			[mount path]
 umount [mount path] ← NOT device path
 partprobe == have linux reload partition table
 ----------------------------------------------
 gdisk /path/to/mount == newer, better. does GPT entries. Do not use on mbr drives or it will automatically convert the mbr to gpt
 >Same steps as fdisk to setup a partition
 ---------------------------------------------
 Physical Drives >> LVG >> LVM >> Application
 LVG == Logical Volume Group. Combination of physical drives as one group.
 LVM == Logical Volume Manager. Works between the OS and physical drive to 	virtually combine physical drives to act together as one.
 
 tl;dr :
 Partition drives as LVM, create physical volumes, create volume group(s), create logical volume(s), mkfs
 >fdisk/gdisk the drives but change partition type to Linux LVM
 pvcreate /path/to/partiton1 /path/to/partition2 …
 vgcreate [volume group name to create] /path/to/partition1 /path/to/partition2 ...
 lvcreate -n [LV name to create] -L [size wanted, ex: 10G] [name of volume group to use]
 >mkfs to setup filesystem to be used
 >mount it somewhere
 
 lvremove /path/to/logical/volume == remove logical volume
 vgremove [volume group name]
 pvremove /path/to/parition1 /path/to/partition2
 
 pvdisplay == view physical volumes
 vgdisplay == view volume groups
 lvdisplay == view logical volumes
 
 To add physical volumes to a group volume:
 vgextend [group name] /path/to/partition
 To remove physical volumes from a group volume:
 vgreduce [groupname] /path/to/partition
 
 To extend logical volume:
 lvextend -L [# in B/M/G] /path/to/logicalvolume
 	>can use -l to specify extends instead of specific disk space)
 	>if no + is used before # then you're changing the max, otherwise a + 	means you want to grow the partition by that amount
 
 This extends size of volume, not size of filesystem, so:
 for xfs: xfs_growfs /path/to/mount
 	(remember xfs cannot be shrunk!)
 for ext: resize2fs /path/to/mount
 
 --------------------------------------------------------------
 xfs_admin (for xfs) // tune2fs (for ext)
 	-L [name] /path/to/partition == label partition
 	-l /path/to/partition == show label name
 /etc/fstab == persistent mounts; self-explanatory; (each separated by a space or tab)
 UUID= or LABEL= or /path/to/partition		mount point		filesystem_type	defaults	1 #
 -----------------------------------------------------------------
 To make swap:
 	from logical volume: pvcreate, vgcreate, lvcreate
 	OR
 	from physical mount: partition like normal, but using swap as type/system id
 Then mkswap [/path/to/volume-group/logical-group] or [/path/to/parition]
 swapon/swapoff /path/to/mount/ == swapon is NOT persistent
 For persistence, in fstab:
 	UUID=xxxxx		swap		swap		0 0
 swapon/swapoff -a == mount/unmount all swaps
 -----------------------------------------------------------------
 dumpe2fs == dump a bunch of info on the partition
 xfs == parallel processing, throughput
 vfat == deprecated, but accessible by windows + linux
 ext4 == default for new linux based OS
 -----------------------------------------------------------------
 CIFS == common internet file system, creating shares among internet/intranet
 	(ex: samba)
 NFS == network file system
 yum install cifs-utils nfs-utils
 CIFS:
 Temporary
 mount -t cifs -o username=xxxx //server_IP/sharename /path/to/mount
 Persistant (fstab) (following way is insecure but it passes RHCSA)
 //server_IP/sharename	/path/to/local/mount	cifs	username=xxxx,password=xxxx	0 0
 NFS:
 Temporary
 mount -t nfs server_IP:/shareroot /path/to/mount
 Persistant (fstab)
 server_IP:/remote/mount/location	/local/mount/destination	nfs	defaults	0 0
 Test these with: mount -a  (after manual umount)
 
 OTHER
 cat /proc/cpuinfo == show system/cpu info
 In RHEL 7.0, you could write:
 # nmcli con mod myConn ipv4.addresses "10.0.0.10/24 10.0.0.1"
 Since RHEL 7.1, you have to do it in two steps:
 # nmcli con mod myConn ipv4.addresses 10.0.0.10/24
 # nmcli con mod myConn ipv4.gateway 10.0.0.1