samankhalife / linux-tutorial

Linux commands and basic concepts you need for performing essential tasks on a server as a DevOps, SRE, or SysAdmin are critical. I'll do my best to explain everything as simple as possible.

linux-Tutorial (with some SRE's info)

linux commands and any thing basic you need yo know for using linux (for cloud computing) it is for my own Knowledge but if you want to use I try to make it very complex and from base so you can learn linux so easy and work on linux based systems.

Contents (Not-Only-In-This-Page)

please 🙏 click on each link cause every thing is not on this page it is more than you think 😜😜😜

• Quick-review-important-commants
• full-list-for-all-Commands
• tree-of-repo
• Exams-Objectives-and-samples:
  • LPIC1
  • LPIC2
  • LPIC3
• How-To-do-some-installation-and-linux-tricks
• Deep-into-linux
• Working-with-cli-editor
• Working-with-git-cli

Common commands preview

• [View Linux command help information] - commands：help, whatis, info, which, whereis, man
• [Linux file directory management] -commands：cd, ls, pwd, mkdir, rmdir, tree, touch, ln, rename, stat, file, chmod, chown, locate, find, cp, mv, rm
• [Linux file content viewing command] - commands：cat, head, tail, more, less, sed, vi, grep
• [Linux File Compression and Decompression] -commands：tar, gzip, zip, unzip
• [Linux User Management] - commands：groupadd, groupdel, groupmod, useradd, userdel, usermod, passwd, su, sudo
• [Linux System Administration ] - commands：reboot, exit, shutdown, date, mount, umount, ps, kill, systemctl, service, crontab
• [Linux Network Administration] - commands：curl, wget, telnet, ip, hostname, ifconfig, route, ssh, ssh-keygen, firewalld, iptables, host, nslookup, nc, netcat, ping, traceroute, netstat
• [Linux Hardware Management ] - commands：df, du, top, free, iotop
• [Linux Software Management ] - commands：rpm, yum, apt-get

try wtf in linux to see the one line describe about commands like this:

wtf ls
wtf mkdir

Linux Getting Started Overview

• Kernel operating system
• Drivers
• System software
• Application software
• Application software with graphical interface

• Application software with graphical interface

More info about Linux kernel

Linux kernel map

Linux Boot Process

• There are 6 stages of the Linux boot process

Stage 1: BIOS (Basic Input/Output System)

• Bios stands for basic input/output system.
• This is the first step of the boot process, Bios doing the POST (Power-on Self-test) job.
• POST is a process of checking the properties.
• When the BIOS process is successful, the BIOS will search and boot an operating system contained in devices such as hard drives, CD/DVD, USB.
• Normally, the BIOS will check the floppy or CD-ROM drives to see if they can boot from them, then the hardware, the order of checking the drives depends on the configuration in the BIOS .
  • If the BIOS can't find it boot device it will report No boot device found.
  • If the operating system Linux is installed on the hard disk, it will find the Master Boot Record at the first sector of the first hard drive.

Stage 2: MBR loading

• MBR (Master Boot Record) is stored in the first sector of a data storage device ( /dev/sda, /dev/hda).
• MBR is very small, only 512byte=1 sector.
• The MBR contains the following information:
  • Primary boot loader code (446 byte) : provides information for boot loaderand location boot loaderand the hard drive.
  • Partition table information ( 64 byte) : stores information about partition.
  • Magic number ( 2 byte) : used to check MBR , if MBR fails, it will restore.

Stage 3: GRUB Loader

• After locating the Boot Loader , this step will execute load the Boot Loader into memory and read the configuration - information then display the GRUB Boot Menu for the user to choose from.
• If the User does not select the OS, after a preset time, GRUB will load the default Kernel into memory to boot.

Stage 4: Kernel

• The operating system's kernel will be loaded into RAM -> When the kernel works, the first thing will execute the INIT process.

Stage 5: Run Level (INIT)

• This is the main stage of the process boot.

       Table 1. Mapping between runlevels and systemd targets
       ┌───────────────────────────────────────┐
       │Runlevel    │ Target            │      │
       ├───────────────────────────────────────┤
       │0           │ poweroff.target   │      │
       ├───────────────────────────────────────┤
       │1           │ rescue.target     │      │
       ├───────────────────────────────────────┤
       │2, 3, 4     │ multi-user.target │      │
       ├───────────────────────────────────────┤
       │5           │ graphical.target  │      │
       ├───────────────────────────────────────┤
       │6           │   reboot.target   │      │
       └───────────────────────────────────────┘

• Run level0 : halt - Shutdown system
• Run level1 : single-user mode -No network configuration, start processes and allow loginuser non-root
• Run level2 : multi-user mode -no network configuration, start processes.
• Run level3 : multi-user mode with networking -boots the system normally on the command line interface.
• Run level4 : undefined
• Run level5 : X11- start the system on the graphical interface
• Run level6 : reboot- reboot the system.

Stage 6: User Prompt

• User login and use.

for-deeper-view-of-kernel-click

Shell

Concepts

• Shell is a program that executes commands from users or applications - the utility requires passing to Kernel for processing.
• Activities of Shell:
  • 1: Command parsing.
  • 2: Interpreting the command's request.
  • 3: Pass message to Kernel.
  • 4: Display the result of the command.

Types of Shell

• sh(the Bourne Shell)
  • Do not autocomplete file names
  • Do not save the typed statement in memory (history)
• bash (Bourne-Again Shell)
  • Linux defaults.
  • Support more commands.
• csh (the C shell)
  • Written in C . programming language.

Shell Prompt (Shell Prompt)

• Is a character or a character set that always starts at the beginning of any command line.
• Indicates that shell is ready to receive commands from the user.
• $: ordinary user
• #: user root

Things you should know about Linux Partitions

1.Hard drives

• As a data storage device, for example in Linux it isdev/sda
• /dev/sda3 is the 3rd primary partition on the first disk
• /dev/sdb5 is the first logical partition on the second disk
• /dev/sda7 is the 3rd logical partition of the first physical disk

2. Partition

• Partition is a small partition (Logical Partition) divided fromHard drives
• Each Hard driveshas 4 partition, in which partition includes 3 types: Primary partition , Extended partition and Logical Partition
• Primary partition +The primary partition can be used to boot the operating system.
• Extended partition +Is the remaining data area when we divide into Primary partitions. +Extended partition contains Logical Partitions in it. Each drive can only hold 1 Extended partition. +Logical partition : These are small partitions in the extended partition , usually used to store data.

fdisk

root@saman:~# fdisk /dev/sda
Welcome to fdisk (util-linux 2.25.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


root@saman:~# Command (m for help): p
Disk /dev/sda: 298.1 GiB, 320072933376 bytes, 625142448 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x000beca1

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sda1  *         2048  43094015  43091968  20.6G 83 Linux
/dev/sda2        43094016  92078390  48984375  23.4G 83 Linux
/dev/sda3        92080126 625141759 533061634 254.2G  5 Extended
/dev/sda5        92080128 107702271  15622144   7.5G 82 Linux swap / Solaris
/dev/sda6       107704320 625141759 517437440 246.8G 83 Linux

parted

root@saman:~# sudo parted /dev/sda p
Model: ATA ST320LT000-9VL14 (scsi)
Disk /dev/sda: 320GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type      File system     Flags
 1      1049kB  22.1GB  22.1GB  primary   ext4            boot
 2      22.1GB  47.1GB  25.1GB  primary   ext4
 3      47.1GB  320GB   273GB   extended
 5      47.1GB  55.1GB  7999MB  logical   linux-swap(v1)
 6      55.1GB  320GB   265GB   logical

• LVM (logical volume management)

In many cases, you need to resize your partitions or even install new disks and add them to your current mount points; Increasing the total size. LVM is designed for this. + Physical Volume (PV): A whole drive or a partition. It is better to define partitions and not use whole disks - unpartitioned. + Volume Groups (VG): This is the collection of one or more PVs. OS will see the vg as one big disk. PVs in one VG, can have different sizes or even be on different physical disks. + Logical Volumes (LV): OS will see lvs as partitions. You can format an LV with your OS and use it.

• To find a file with a larger size, you can use the du (Disk Usage) and sort commands. In the command line, run the following

du -h /path/to/directory | sort -rh

MBR and GPT

• Information about hard disk partitions will be stored on MBR (Master Boot record) or GPT (GUID Partition table).
• These are two standards for configuring and managing Partitions on hard drives.
• The information stored here includes the location and size of the Partitions.

Swap file

• Swap is virtual memory concept used on Linux.
• When VPS/Serveroperating, if the system runs out of RAM, it will automatically use part of the hard drive as memory for applications to operate.
• Swap is slower than RAM because Swap is part of the hard drive.
• (mostly we set swap 2_ram but less than 8 GB for hdd and set 1_ram or 2*ram )

These are some of the most used bash environment variables

USER	The name of the logged-in user
PATH	List of directories to search for commands, colon separated
EDITOR	Default editor
HISTFILE	System hostname
HOSTNAME	Show Info
PS1	The Prompt! Play with it
UID	The numeric user id of the logged-in user
HOME	The user's home directory
PWD	The current working directory
SHELL	The name of the shell
$	The process id (or PID of the running bash shell (or other) process
PPID	The process id of the process that started this process (that is, the id of the parent process)
?	The exit code of the last command

File Directory

• /home – User personal data
• /boot – Static files of the boot loader
• /sbin – System binaries
• /dev – Device files
• /sys
• /etc – Configuration files
• /proc – Process and kernel files
• /var – Variable data files
  • /tmp – Temporary files
  • /lock
  • /log
• /usr – User binaries and program data
  • /bin – Binaries
  • /man
  • /lib – Shared libraries
  • /local
  • /share
• /opt – Optional software
• /root – The home directory of the root
• /media – Mount point for removable media
• /mnt – Mount point for mounting a filesystem temporarily
• /srv – Service data

All default Linux commands in bin dir

VIEW ALL

for better view you can see the code----------------------------------------------------------------------------------------------------------- envsubst lslogins rgrep systemd-cryptenroll VGAuthService eqn lsmem rlogin systemd-delta '[' ex lsmod rm systemd-detect-virt aa-enabled expand lsns rmdir systemd-escape aa-exec expiry lsof rnano systemd-hwdb aa-features-abi expr lspci routef systemd-id128 add-apt-repository factor lspgpot routel systemd-inhibit addpart faillog lspower rrsync systemd-machine-id-setup addr2line fallocate lsusb rsh systemd-mount apport-bug false lzcat rsync systemd-notify apport-cli fgconsole lzcmp rsync-ssl systemd-path apport-collect fgrep lzdiff rtstat systemd-repart apport-unpack file lzegrep run-one systemd-run apropos finalrd lzfgrep run-one-constantly systemd-socket-activate apt fincore lzgrep run-one-until-failure systemd-stdio-bridge apt-add-repository find lzless run-one-until-success systemd-sysext apt-cache findmnt lzma run-parts systemd-sysusers apt-cdrom flock lzmainfo run-this-one systemd-tmpfiles apt-config fmt lzmore runcon systemd-tty-ask-password-agent apt-extracttemplates fold mailmail3 rview systemd-umount apt-ftparchive free man rvim tabs apt-get ftp man-recode savelog tac apt-key fuser mandb sbattach tail apt-mark fusermount manifest sbkeysync tar apt-sortpkgs fusermount3 manpath sbsiglist taskset ar gapplication mapscrn sbsign tbl arch gawk mawk sbvarsign tclsh as gdbus mcookie sbverify tclsh8.6 automat-visualize3 geqn md5sum scandeps tcpdump awk getconf md5sum.textutils scp tee b2sum getent mdig screen telnet base32 getkeycodes mesg screendump telnet.netkit base64 getopt migrate-pubring-from-classic-gpg script tempfile basename gettext mk_modmap scriptlive test basenc gettext.sh mkdir scriptreplay tic bash ginstall-info mkfifo scsi_logging_level time bashbug gio mknod scsi_mandat timedatectl bc gio-querymodules mksquashfs scsi_readcap timeout boltctl git mktemp scsi_ready tkconch3 btrfs git-receive-pack mokutil scsi_satl tload btrfs-convert git-shell more scsi_start tmux btrfs-find-root git-upload-archive mount scsi_stop tnftp btrfs-image git-upload-pack mountpoint scsi_temperature toe btrfs-map-logical glib-compile-schemas mt sdiff top btrfs-select-super gold mt-gnu sed touch btrfsck gp-archive mtr select-editor tput btrfstune gp-collect-app mtr-packet sensible-browser tr busctl gp-display-html mv sensible-editor tracepath busybox gp-display-src namei sensible-pager trial3 byobu gp-display-text nano seq troff byobu-config gpasswd nawk setarch true byobu-ctrl-a gpg nc setfont truncate byobu-disable gpg-agent nc.openbsd setkeycodes tset byobu-disable-prompt gpg-connect-agent neqn setleds tsort byobu-enable gpg-wks-server netcat setlogcons tty byobu-enable-prompt gpg-zip networkctl setmetamode twist3 byobu-export gpg2 networkd-dispatcher setpci twistd3 byobu-janitor gpgcompose newgrp setpriv tzselect byobu-keybindings gpgconf ngettext setsid ua byobu-launch gpgparsemail nice setterm ubuntu-advantage byobu-launcher gpgsm nisdomainname setupcon ubuntu-bug byobu-launcher-install gpgsplit nl sftp ubuntu-core-launcher byobu-launcher-uninstall gpgtar nm sg ubuntu-distro-info byobu-layout gpgv nohup sg_bg_ctl ubuntu-security-status byobu-prompt gpic nproc sg_compare_and_write ucf byobu-quiet gprof nroff sg_copy_results ucfq byobu-reconnect-sockets gprofng nsenter sg_dd ucfr byobu-screen grep nslookup sg_decode_sense uclampset byobu-select-backend gresource nstat sg_emc_trespass udevadm byobu-select-profile groff nsupdate sg_format ul byobu-select-session grog ntfs-3g sg_get_config umount byobu-shell grops ntfs-3g.probe sg_get_elem_status uname byobu-silent grotty ntfscat sg_get_lba_status unattended-upgrade byobu-status groups ntfscluster sg_ident unattended-upgrades byobu-status-detail growpart ntfscmp sg_inq uncompress byobu-tmux grub-editenv ntfsdecrypt sg_logs unexpand byobu-ugraph grub-file ntfsfallocate sg_luns unicode_start byobu-ulevel grub-fstest ntfsfix sg_map unicode_stop c++filt grub-glue-efi ntfsinfo sg_map26 uniq c_rehash grub-kbdcomp ntfsls sg_modes unlink captoinfo grub-menulst2cfg ntfsmove sg_opcodes unlzma cat grub-mkfont ntfsrecover sg_persist unmkinitramfs catman grub-mkimage ntfssecaudit sg_prevent unshare cftp3 grub-mklayout ntfstruncate sg_raw unsquashfs chage grub-mknetdir ntfsusermap sg_rbuf unxz chardet grub-mkpasswd-pbkdf2 ntfswipe sg_rdac unzstd chardetect grub-mkrelpath numfmt sg_read update-alternatives chattr grub-mkrescue objcopy sg_read_attr update-mime-database chcon grub-mkstandalone objdump sg_read_block_limits uptime chfn grub-mount od sg_read_buffer usb-devices chgrp grub-ntldr-img oem-getlogs sg_read_long usbhid-dump chmod grub-render-label on_ac_power sg_readcap usbreset choom grub-script-check openssl sg_reassign users chown grub-syslinux2cfg openvt sg_referrals utmpdump chrt gsettings os-prober sg_rep_pip uuidgen chsh gtbl pager sg_rep_zones uuidparse chvt gunzip partx sg_requests vcs-run ckbcomp gzexe passwd sg_reset vdir ckeygen3 gzip paste sg_reset_wp vi cksum h2ph pastebinit sg_rmsn view clear h2xs patch sg_rtpg vigpg clear_console hardlink pathchk sg_safte vim cloud-id hd pbget sg_sanitize vim.basic cloud-init head pbput sg_sat_identify vim.tiny cloud-init-per helpztags pbputs sg_sat_phy_event vimdiff cmp hexdump pdb3 sg_sat_read_gplog vimtutor codepage host pdb3.10 sg_sat_set_features vm-support col hostid peekfd sg_scan vmhgfs-fuse col1 hostname perl sg_seek vmstat col2 hostnamectl perl5.34-x86_64-linux-gnu sg_senddiag vmtoolsd col3 htop perl5.34.0 sg_ses vmware-alias-import col4 hwe-support-status perlbug sg_ses_microcode vmware-checkvm col5 i386 perldoc sg_start vmware-hgfsclient col6 iconv perlivp sg_stpg vmware-namespace-cmd col7 id perlthanks sg_stream_ctl vmware-rpctool col8 info pgrep sg_sync vmware-toolbox-cmd col9 infobrowser pic sg_test_rwbuf vmware-vgauth-cmd colcrt infocmp pico sg_timestamp vmware-vmblock-fuse colrm infotocap piconv sg_turs vmware-xferlogs column install pidof sg_unmap w comm install-info pidwait sg_verify wall conch3 instmodsh pinentry sg_vpd watch corelist ionice pinentry-curses sg_wr_mode watchgnupg cp ip ping sg_write_buffer wc cpan ipcmk ping4 sg_write_long wdctl cpan5.34-x86_64-linux-gnu ipcrm ping6 sg_write_same wget cpio ipcs pinky sg_write_verify whatis crontab iptables-xml pkaction sg_write_x whereis csplit ischroot pkcheck sg_xcopy which ctail iscsiadm pkcon sg_zone which.debianutils ctstat join pkexec sginfo whiptail curl journalctl pkill sgm_dd who cut jq pkmon sgp_dd whoami cvtsudoers json-patch-jsondiff pkttyagent sh wifi-status dash json_pp pl2pm sha1sum write date jsondiff pldd sha224sum x86_64 dbus-cleanup-sockets jsonpatch plymouth sha256sum x86_64-linux-gnu-addr2line dbus-daemon jsonpointer pmap sha384sum x86_64-linux-gnu-ar dbus-monitor jsonschema pod2html sha512sum x86_64-linux-gnu-as dbus-run-session kbd_mode pod2man shasum x86_64-linux-gnu-c++filt dbus-send kbdinfo pod2text showconsolefont x86_64-linux-gnu-dwp dbus-update-activation-environment kbxutil pod2usage showkey x86_64-linux-gnu-elfedit dbus-uuidgen keep-one-running podchecker shred x86_64-linux-gnu-gold dd kernel-install pollinate shuf x86_64-linux-gnu-gp-archive deallocvt keyring pr size x86_64-linux-gnu-gp-collect-app deb-systemd-helper kill preconv skill x86_64-linux-gnu-gp-display-html deb-systemd-invoke killall printenv slabtop x86_64-linux-gnu-gp-display-src debconf kmod printf sleep x86_64-linux-gnu-gp-display-text debconf-apt-progress kmodsign prlimit slogin x86_64-linux-gnu-gprof debconf-communicate landscape-sysinfo pro snap x86_64-linux-gnu-gprofng debconf-copydb last prove snapctl x86_64-linux-gnu-ld debconf-escape lastb prtstat snapfuse x86_64-linux-gnu-ld.bfd debconf-set-selections lastlog ps snice x86_64-linux-gnu-ld.gold debconf-show lcf psfaddtable soelim x86_64-linux-gnu-nm debian-distro-info ld psfgettable sort x86_64-linux-gnu-objcopy delpart ld.bfd psfstriptable sos x86_64-linux-gnu-objdump delv ld.gold psfxtable sos-collector x86_64-linux-gnu-ranlib df ldd pslog sosreport x86_64-linux-gnu-readelf dh_bash-completion less pstree splain x86_64-linux-gnu-size diff lessecho pstree.x11 split x86_64-linux-gnu-strings diff3 lessfile ptar splitfont x86_64-linux-gnu-strip dig lesskey ptardiff sqfscat xargs dir lesspipe ptargrep sqfstar xauth dircolors lexgrog ptx ss xdg-user-dir dirmngr libnetcfg purge-old-kernels ssh xdg-user-dirs-update dirmngr-client link pwd ssh-add xsubpp dirname linux-boot-prober pwdx ssh-agent xxd distro-info linux-check-removal py3clean ssh-argv0 xz dmesg linux-update-symlinks py3compile ssh-copy-id xzcat dnsdomainname linux-version py3versions ssh-import-id xzcmp do-release-upgrade linux32 pybabel ssh-import-id-gh xzdiff domainname linux64 pybabel-python3 ssh-import-id-lp xzegrep dpkg ln pydoc3 ssh-keygen xzfgrep dpkg-deb lnstat pydoc3.10 ssh-keyscan xzgrep dpkg-divert loadkeys pygettext3 stat xzless dpkg-maintscript-helper loadunimap pygettext3.10 static-sh xzmore dpkg-query locale pyhtmlizer3 stdbuf yes dpkg-realpath locale-check pyserial-miniterm strace ypdomainname dpkg-split localectl pyserial-ports strace-log-merge zcat dpkg-statoverride localedef python3 streamzip zcmp dpkg-trigger logger python3.10 strings zdiff du login pzstd strip zdump dumpkeys loginctl ranlib stty zegrep dwp logname rbash su zfgrep eatmydata look rcp sudo zforce ec2metadata lowntfs-3g rdma sudoedit zgrep echo ls readelf sudoreplay zipdetails ed lsattr readlink sum zless editor lsb_release realpath sync zmore efibootdump lsblk red systemctl znew efibootmgr lscpu renice systemd zstd egrep lsfd rescan-scsi-bus.sh systemd-analyze zstdcat eject lshw reset systemd-ask-password zstdgrep elfedit lsinitramfs resizecons systemd-cat zstdless enc2xs lsipc resizepart systemd-cgls zstdmt encguess lsirq resolvectl systemd-cgtop env lslocks rev systemd-creds

User Permissions and attributes

command	what it means	what it does	how to use it
chmod	change modifiers	edits the permissions of a file	chmod +x filename
chattr	change attributes	edits the attributes of a file	chattr +i filename
chown	change owner

chmod is used to edit the permissions on a file. There are 3 permissions and 3 groups, for a total of 9 permissions. The permissions are:

• read - allows the group to read the file
• write - allows the group to edit the file
• execute - allows the group to run the file as a program

for example when using ls -la you see all of the files permissions

(user)
 |   
 |     
 |     (others)
 |     |
-rw-r--r-- 1 username groupname date time ...
    |
    |
   (group) 

so this file the owner has rw, the group has r and everyone has r

to make a file executable for all users you would run the following command

chmod a+x filename

character	group name	who it applies to
u	user	the owner of the file
g	group	users who are members of the files' group
o	others	users not included in u or g
a	all	u, g and o

chmod can take either a set of three octal (base 8) numbers to set the permissions across all groups, or list the groups "a+" and the permissions that you want to add or "a-" and the permissions you want to subtract.

The character representations of the permissions are:

letter	number	binary	permission
r	4	100	read
w	2	010	write
x	1	001	execute

So chmod a+rwx filename is the same as chmod 777 filename

• examples:
• chmod u+x,g+w filename
• chmod u=rwx,g=rw,o=r filename
• chmod 764 filename
• chmod a+x filename

The chown command changes the owner and group of a file or directory. This command can authorize a user to become the owner of the specified file or change the group to which the file belongs. User can be user or user D, user group can be group name or group id. The filename can be a list of files separated by spaces, and wildcards can be included in the filename.

Only the file owner and superuser can use this command.

Group Permissions and attributes

gorupmod

groupadd

groupdel

groups

apt command in linux (for installing packages)

apt provides a high-level CLI (Command Line Interface) for the package management system and is intended as an interface for the end user which enables some options better suited for interactive usage by default compared to more specialized APT tools like apt-cache and apt-get.

Syntax :apt [...COMMANDS] [...PACKAGES]

update :apt update

full-upgrade :apt full-upgrade

install :apt install [...PACKAGES]

remove :apt remove [...PACKAGES]

purge :apt purge [...PACKAGES]

search :apt search [...REGEX] This command is used when the user wants to search for the given regex term(s) in the list of available packages and display matches. For example, this command can be useful when you want to search for packages having a specific feature.

show :apt show [...PACKAGES]

APT-GET Command in Linux

Basic Syntax :sudo apt-get [options] [command] [package(s)]

If you want to download only one specific package, you can do:apt-get download [...PACKAGES]

Removing debian packages:apt-get remove [package(s)]

package information with dpkg

If you want to reconfigure a package that is already installed, you can use the:dpkg-reconfigure tzdata

dpkg [OPTIONS] ACTION PACKAGE

Switch Description

\

wildcard characters for globbing

Wildcard characters are used in globbing and regular expressions to represent patterns of text. While the exact set of wildcard characters can vary depending on the context and programming language, here are some common wildcard characters and their meanings:

1. Asterisk (*): Matches zero or more characters. It is often used as a wildcard for any sequence of characters.
   • Example: *.txt matches all files ending with ".txt."
2. Question Mark (?): Matches a single character. It is used to represent any character in a specific position.
   • Example: file?.txt matches "file1.txt" and "file2.txt."
3. Square Brackets ([]) and Dash (-) for Character Ranges: Square brackets are used to define character classes, and the dash is used to specify character ranges within those classes.
   • [aeiou] matches any one vowel.
   • [0-9] matches any digit.
   • [A-Za-z] matches any uppercase or lowercase letter.
4. Curly Braces ({}) for Alternatives: Curly braces are used to specify alternative patterns or choices.
   • {jpg,jpeg,png} matches either "jpg," "jpeg," or "png."
5. Exclamation Mark (!) or Caret (^) (Inside Square Brackets): When placed at the beginning of a character class, these symbols negate the class, matching any character not listed in the brackets.
   • [^0-9] matches any character that is not a digit.
6. Period (.): In regular expressions, the period is a wildcard that matches any single character.
   • Example: a.c matches "abc," "adc," etc.
7. Pipe (|) (In Regular Expressions): Represents the logical OR operation and is used to specify alternatives.
   • Example: apple|banana matches either "apple" or "banana."
8. Backslash (\) (Escape Character): In some contexts, the backslash is used to escape special characters, so they are treated as literal characters rather than as wildcards or metacharacters.

These wildcard characters provide flexible ways to match patterns in text and are commonly used in various programming languages, command-line utilities, and regular expressions for tasks such as text searching, text processing, and file manipulation. Keep in mind that the availability and behavior of these characters can vary depending on the specific environment or tool you're using.

more info wildcard characters for globbing

2 Ways to Download Files From Linux Terminal

how do you download a file from the terminal?

1.Download files from Linux terminal using wget command

wget command

Installing wget:

sudo apt install wget

Download a file or webpage using wget:

wget URL

2.Download files from Linux command line using curl

curl command

Installing curl:

sudo apt install curl

Download a file or webpage using curl:

curl URL

How to your find your Linux IP address

The following commands will get you the IP address list to find public IP addresses for your machine:

If you enter the command ifconfig in the terminal, all information will be displayed. You can also use these commands:

The following commands will get you the IP address list to find public IP addresses for your machine:

• curl ifconfig.me
• curl -4/-6 icanhazip.com
• curl ipinfo.io/ip
• curl api.ipify.org
• curl checkip.dyndns.org
• dig +short myip.opendns.com @resolver1.opendns.com
• host myip.opendns.com resolver1.opendns.com
• curl ident.me

The following commands will get you the private IP address of your interfaces:

• ifconfig -a
• hostname -I'
• ip route get 1.2.3.4'
• nmcli -p device show(best option in my opinion)

Linux Networking Tools

ping

host

finger

traceroute

netstat

tracepath

dig

hostname

route

nslookup

SSH

DNS

Firewalls

Here are the Best Firewalls for Linux for Effective System Protection

IPFire

Key Features:

Firewall engine and Instruction Prevention system.

Offers default zones with different security policies. For example, DMZ and LAN.

Frequently updated to prevent attack vectors and security vulnerabilities.

Offers Stateful Package Inspection(SPI) firewall built on top of Netfilter.

Provides an intuitive web user interface.

Protects against Denial-of-Service attacks.

It lets users create logging and graphical reports for insights.

It can be installed on hardware devices such as Raspberry Pi.

IPFire

PfSense

Key Features:

FreeBSD-based.

Supports a wide variety of hardware.

Clean web interface.

It comes with commercial-grade features.

Supports VPN endpoint and wireless access point configuration.

Outbound and Inbound load balancing.

Real-time information.

pfsense

Zenarmor

Key Features:

Web filtering, application control, and cloud threat intelligence.

Auto-block malware/phishing attempts in real-time.

Instantly deploy firewall with minimal setup requirements.

Offers centralized cloud management to manage multiple firewalls.

Improves network visibility with rich analytics and reporting.

Zenarmor

UFW

\

UFW help

IPcop

IPcop docs

Opnsence

\

Opnsence

Surewall

\

Surewall

ClearOS

\

ClearOS

Arista Edge

\

Arista Edge

iptables

iptables is a powerful configuration tool for controlling traffic to and from your system. Modern Linux kernels come with a packet filtering framework called Netfilter. Netfilter provides operations such as allow, drop, and modify to control the flow of packets into and out of the system. The user-level command-line tool iptables based on the Netfilter framework provides a powerful firewall configuration function, allowing you to add rules to build firewall policies. The richness and complexity of iptables and its baroque command syntax can be overwhelming.

main view of iptable command

                                          (chains)
         (table)                             |                                  (source)                                                                                                             MASQURADE
            |                            PREROUTING          1                      |                                                             1                    1                             ACCEPT
            |       filter     -A        INPUT               2            udp       |   xxx.xxx.xxx.xxx            xxx.xxx.xxx.xxx                2                    2             -------         REJECT
iptables   -t       nat        -I        FORWARDING          .     -P     tcp      -S   37.16.2.4           -d     185.674.46.4       --sport     .       --dport      .      -m     module   -J     DROP
                    mangle     -D        OUTPUT              .            icmp                               |                                    .                    .             -------   |     DNAT 
                               -U        POSTROUTING         n                                               |                                  65535                65535                     |     SNAT
                                |                            |                                         (destination)                                                                           |
               (insert)(apend)(delete)(update)               |                                                                                                                 [this is the most important thing]
                                                             |                                                                                                                                         
                                                      (line you want) 

chains that packets will go through in iptable

If you live in countries that are embargoed by some companies and applications, you can use some thing like DNS changing for using the apps.

• shecan
• hostiran
• electrotm
• begzar
• vanillapp
• 403.online

If you dont know how to change and set it follow these steps

• connect to your srver with ssh.

• open /etc/resolv.conf with some editor like nano or vim.

• change the in front of namesrver like this:

  nameserver 172.29.2.100
  nameserver 185.51.200.2
  

• save changes and exit.

How to Check Ubuntu Version Details and Other System Information

type the following command:

lsb_release -a

Alternate way:

cat /etc/lsb-release

Another Fun way:

Neofetch command

Getting SSL Certificat

you can use any kind tools you know here are some of them:

• acme
• zerossl
• free-ssl
• certbot

learn getting free ssl with acme step by step

Some of the server monitoring tools

How To View Running Processes in Linux

• top
• htop
• ps
• lsof

How To Monitor Your Network

• nethogs
• iptraf-ng
• netstat
• iftop
• (speed test)

How To Monitor Your Disk Usage

• df
• du
• iotop
• iostat

How To Monitor Your Memory Usage

• free(Ram usage)
• vmstat

How to to Manage Processes in Linux

• kill
• nice

mosltly use for controlling the cpu usage (nice number is from -20 to 19 ).

Some of the monitoring apps

• prometheus
  • my docs
• grafana
  • my docs
• zabbix
• paessler
• nagios
• elastic.co
• elastic
• influxdata

How To Add Swap Space

What is Swap????? Swap is a portion of hard drive storage that has been set aside for the operating system to temporarily store data that it can no longer hold in RAM. This lets you increase the amount of information that your server can keep in its working memory, with some caveats.

Checking the System for Swap Information

We can see if the system has any configured swap by typing:sudo swapon --show.

If you don’t get back any output, this means your system does not have swap space available currently.

You can verify that there is no active swap using the free utility:free -h

Checking Available Space on the Hard Drive Partition

Before we create our swap file, we’ll check our current disk usage to make sure we have enough space:df -h

Creating a Swap File

Now that we know our available hard drive space, we can create a swap file on our filesystem. We will allocate a file of the size that we want called swapfile in our root (/) directory.

The best way of creating a swap file is with the fallocate program. This command instantly creates a file of the specified size.

Since the server in our example has 1G of RAM, we will create a 1G file in this guide. Adjust this to meet the needs of your own server:sudo fallocate -l 1G /swapfile

We can verify that the correct amount of space was reserved by typing:ls -lh /swapfile

Enabling the Swap File

Now that we have a file of the correct size available, we need to actually turn this into swap space.

First, we need to lock down the permissions of the file so that only users with root privileges can read the contents. This prevents normal users from being able to access the file, which would have significant security implications.

Make the file only accessible to root by typing:sudo chmod 600 /swapfile

Verify the permissions change by typing:ls -lh /swapfile

Output
-rw------- 1 root root 1.0G jul 16 16:18 /swapfile

only the root user has the read and write flags enabled.

We can now mark the file as swap space by typing:sudo mkswap /swapfile

After marking the file, we can enable the swap file, allowing our system to start using it:sudo swapon /swapfile

Verify that the swap is available by typing:sudo swapon --show

Output
NAME      TYPE  SIZE USED PRIO
/swapfile file 1024M   0B   -2

We can check the output of the free utility again to corroborate our findings:free -h

Output
              total        used        free      shared  buff/cache   available
Mem:          981Mi       123Mi       644Mi       0.0Ki       213Mi       714Mi
Swap:         1.0Gi          0B       1.0Gi

Making the Swap File Permanent

Our recent changes have enabled the swap file for the current session. However, if we reboot, the server will not retain the swap settings automatically. We can change this by adding the swap file to our /etc/fstab file.

Back up the /etc/fstab file in case anything goes wrong:sudo cp /etc/fstab /etc/fstab.bak

Add the swap file information to the end of your /etc/fstab file by typing:echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

Next we’ll review some settings we can update to tune our swap space.

Linux as a virtualization guest

topics:Virtual machine/Linux container/Application container/Guest drivers/SSH host keys/D-Bus machine id

To check and see if your host operating system / CPU, supports using hypervisors check for the vmx (for Intel CPUs) or svm (for AMD CPUs) in your /proc/cpuinfo in flags.

Based on your CPU you should have kvm or kvm-amd kernel modules loaded.

lsmod | grep -i kvm
sudo modprobe kvm

(If you see hypervisor in your /proc/cpuinfo it means that you are inside a virtualized Linux machine )

let's see the 2 types of hypervisors. First type 2, since it's easier to understand.

Type 2 Hypervisor

These hypervisors run on a conventional operating system (OS) just as other computer programs do. A guest operating system runs as a process on the host. Type-2 hypervisors abstract guest operating systems from the host operating system.

In other words, a type 2 hypervisor is the software between the guest and host. It completely runs on the host OS and provides virtualization to the guest.

Two of the most famous Type 2 hypervisors are VirtualBox (from Oracle) and VMware.

Type 1 Hypervisor

These hypervisors run directly on the host's hardware to control the hardware and manage guest operating systems. For this reason, they are sometimes called bare-metal hypervisors. The first hypervisors, which IBM developed in the 1960s, were native hypervisors. These included the test software SIMMON and the CP/CMS operating system, the predecessor of IBM z/VM.

Some of the most famous Type 1 hypervisors are KVM, Xen & Hyper-V. KVM is built-in since Linux Kernel version 2.6.20.

Creating a Virtual Machine

First, create the machine itself. We tell the hypervisor this machine how much RAM/disk/CPU/... needs and set a name for our machine. Then we need to install the guest OS. This can be done using:

• Installing from a CD / DVD / ...
• Cloning an existing machine.
• Using Open Virtualization Format (OVF) to move machines between hypervisors. This is a standard format for virtual machine definition and may include several files, in this case, you can archive all of them into one Open Virtualization Archive (OVA) file.
• It is also possible to create Templates that are master copies* to initiate new machines.

Guest-specific configs

Some configurations are machine specific. For example, a network card's MAC address should be unique for whole the network. If we are cloning a machine or sometimes creating them from templates, at least we need to change these on each machine before booting them:

• Host Name
• NIC MAC Address
• NIC IP (If not using DHCP)
• Machine ID (delete the /etc/machine-id and /var/lib/dbus/machine-id and run dbus-uuidgen --ensure. These two files might be soft links to each other)
• Encryption Keys like SSH Fingerprints and PGP keys
• HDD UUIDs
• Any other UUIDs on the system

Some info about Clouds and SRE things

Cloud Delivery Models

Infrastructure as a Service (IaaS)

IaaS is the on-demand delivery of computing infrastructure, including operating systems, networking, storage, and other infrastructural components. Acting much like a virtual equivalent to physical servers, IaaS relieves cloud users of the need to buy and maintain physical servers while also providing the flexibility to scale and pay for resources as needed. IaaS is a popular option for businesses that wish to leverage the advantages of the cloud and have system administrators who can oversee the installation, configuration, and management of operating systems, development tools, and other underlying infrastructure that they wish to use. However, IaaS is also used by developers, researchers, and others who wish to customize the underlying infrastructure of their computing environment. Given its flexibility, IaaS can support everything from a company’s computing infrastructure to web hosting to big data analysis.

Platform as a Service (PaaS)

PaaS provides a computing platform where the underlying infrastructure (such as the operating system and other software) is installed, configured, and maintained by the provider, allowing users to focus their efforts on developing and deploying apps in a tested and standardized environment. PaaS is commonly used by software developers and developer teams as it cuts down on the complexity of setting up and maintaining computer infrastructure, while also supporting collaboration among distributed teams. PaaS can be a good choice for developers who don’t have the need to customize their underlying infrastructure, or those who want to focus their attention on development rather than DevOps and system administration.

Software as a Service (SaaS)

SaaS providers are cloud-based applications that users access on demand from the internet without needing to install or maintain the software. Examples include GitHub, Google Docs, Slack, and Adobe Creative Cloud. SaaS applications are popular among businesses and general users given that they’re often easy to adopt, accessible from any device, and have free, premium, and enterprise versions of their applications. Like PaaS, SaaS abstracts away the underlying infrastructure of the software application so that users are only exposed to the interface they interact with.

Cloud Environments

Public Cloud

The public cloud refers to cloud services (such as virtual machines, storage, or applications) offered publicly by a commercial provider to businesses and individuals. Public cloud resources are hosted on the commercial provider’s hardware, which users access through the internet. They are not always suitable for organizations in highly-regulated industries, such as healthcare or finance, as public cloud environments may not comply with industry regulations regarding customer data.

Private Cloud

The private cloud refers to cloud services that are owned and managed by the organization that uses them and available only to the organization’s employees and customers. Private clouds allow organizations to exert greater control over their computing environment and their stored data, which can be necessary for organizations in highly-regulated industries. Private clouds are sometimes seen as more secure than public clouds as they are accessed through private networks and enable the organization to directly oversee their cloud security. Public cloud providers sometimes provide their services as applications that can be installed on private clouds, allowing organizations to keep their infrastructure and data on premise while taking advantage of the public cloud’s latest innovations.

Hybrid Cloud and Multicloud

Many organizations use a hybrid cloud environment which combines public and private cloud resources to support the organization’s computing needs while maintaining compliance with industry regulation. Multicloud environments are also common, which entail the use of more than one public cloud provider (for example, combining Amazon Web Services and DigitalOcean).

Managed cloud

Managed cloud services refer to cloud computing solutions in which a third-party provider takes on the responsibility of managing various aspects of your cloud infrastructure, applications, and services.

Micro cloud

Micro clouds are a new class of infrastructure for on-demand computing at the edge. They differ from the internet-of-things (IoT), which uses thousands of single machines or sensors to gather data, yet they perform computing tasks. Micro clouds reuse proven cloud primitives but with the unattended, autonomous and clustering features that resolve typical edge computing challenges.

Multi-cloud

Multi-cloud (also referred to as multi cloud or multicloud) is a concept that refers to using multiple clouds from more than one cloud service provider at the same time. The term is also used to refer to the simultaneous running of bare metal, virtualised and containerised workloads.

SLA(Service Level agreement) / SLI(Service Level Indicators) / SLO(Service Level Objectives)

If the running time and availability of a system cannot be measured, it is very difficult to maintain and operate the system that is already online, which often causes the maintenance and operation team to continue to be in the state of a fire brigade, and when the root cause of the problem is finally found, it may be the development There is a problem with the code written by the team.

Development teams often don't see "stability" as a potential problem if they can't figure out how to measure runtime and availability. This problem has plagued Google for many years, which is why the SRE principle was developed. One of the motivations.

SRE ensures that everyone knows how to measure reliability and what to do when a service fails. This will be detailed to the point that when a problem occurs, from VP or CxO to every relevant employee within the organization, they all have to do what they should do. What each "person" should do is clearly regulated. SRE will communicate with all relevant personnel to determine Service Level Indicators (SLIs) and Service Level Objectives (SLOs).

SLIs define metrics related to the "response time" of a system, such as response time, throughput per second, requests, etc., and often convert this metric into a ratio or average.

SLOs are a time interval obtained after discussions with relevant personnel. It is expected that SLIs can maintain a certain level of figures, such as "what is the level of SLIs every month", which is more internal indicators.

The video also discusses Service Level Agreements (SLAs), even though it's not a number that SREs care about on a daily basis. As an online service provider, SLA is a commitment to customers to ensure that the percentage of continuous operation of the service is usually "negotiated" with customers, and the downtime per year (or month) should not be less than a few minutes.

The concepts of SLI, SLO, and SLA are very similar to the "everything can be measured" mentioned by DevOps, which is one of the reasons why it is said that class SRE implements DevOps.

Uptime

Availability %	Downtime per year	Downtime per month	Downtime per Week
90%	36.5 days	72 hours	16.8 hours
95%	18.25 days	36 hours	8.4 hours
98%	7.30 days	14.4 hours	3.36 hours
99%	3.65 days	7.20 hours	1.68 hours
99.5%	1.83 days	3.60 hours	50.4 minutes
99.8%	17.52 hours	86.23 minutes	20.16 minutes
99.9%	8.76 hours	43.2 minutes	10.1 minutes
99.95%	4.38 hours	21.56 minutes	5.04 minutes
99.99%	52.6 minutes	4.32 minutes	1.01 minutes
99.999%	5.26 minutes	25.9 seconds	6.05 seconds
99.9999%	31.5 seconds	2.59 seconds	0.605 seconds

Mean Time To Recover (MTTR)

MTTR is the average time that a device will take to recover from any failure.

Mean Time Between Failures (MTBF)

MTBF is the predicted elapsed time between inherent failures of a mechanical or electronic system, during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a system. The term is used for repairable systems, while mean time to failure (MTTF) denotes the expected time to failure for a non-repairable system.

Mean Time To Failure (MTTF)

MTTF denotes the expected time to failure for a non-repairable system.

Critical incident response time (CIRT)

Critical incident response time (CIRT) is a new, significantly more accurate method to evaluate operations performance. CIRT focuses on the incidents that are most likely to impact business by culling noise from incoming signals using the following techniques:

Real business-impacting (or potentially impacting) incidents are very rarely low urgency, so rule out all low-urgency incidents.

Real business-impacting incidents are very rarely (if ever) auto-resolved by monitoring tools without the need for human intervention, so rule out incidents that were not resolved by a human.

Short, bursting, and transient incidents that are resolved within 120 seconds are highly unlikely to be real business-impacting incidents, so rule them out.

Incidents that go unnoticed, tabled, or ignored (not acknowledged, not resolved) for a very long time are rarely business-impacting; rule them out. Note:

This threshold can be a statistically derived number that is customer-specific (e.g., two standard deviations above the mean) to avoid using an arbitrary number.

Individual, ungrouped incidents generated by separate alerts are not representative of the larger business-impacting incident. Therefore, simulate incident

groupings with a very conservative threshold, e.g., two minutes, to calculate response time.

books that you need to read as sre

• incident-management
• Building Secure & Reliable Systems
• The Site Reliability Workbook
• Site Reliability Engineering

Sources I get help from

• Digital ocean
• google youtube chanel
• some open source projects

linux-tutorial's Issues

Create a 'digital book' using markdown

Hi, I'm interested in this repository. In my opinion, you could try gitbook or mdbook or other digital books that can be written with markdown. So users can freely read and explore the articles you write.