UNICS (UNiplexed Information Computing System), Unix, Unix Ware, SCO Unix, BSD, Free BSD, Net BSD, DragonFly BSD, System III, System V, Minix, Xenix, SCO-Xenix, POSIX, HP-UX, AIX, Solaris, Open Solaris, Sun OS, NexTStep / OPENSTEP, GNU, Linux, (Kali, Debian, Android, Scientific Linux, Fedora, CentOS, Mandrake, SUSE[Gecko, Studio], UBUNTU [Gubuntu, Lubuntu, Edubuntu, Mythbuntu, Ubuntu GNOME, Ubuntu MATE], Red Hat, Arch Linux, Bodhi Linux), Open Server, IRIX, Mac OS, OS X etc …
There are so many Unix and Unix like systems so far. Check out https://commons.wikimedia.org/wiki/File:Unix_timeline.en.svg and https://upload.wikimedia.org/wikipedia/commons/7/77/Unix_history-simple.svg for comprehensive beautiful charts.
Linux is open source, community driven & portable unlike Unix and it has more flavors, better GUI, larger number of users, faster Bug-Fix-Support, lesser viruses, supports more file systems compared to all that of Unix which makes Linux more popular.
FYI all the CLI (Command Line Interface) commands below are tried & tested successfully on Ubuntu 20.04.2 LTS. Some of them may or may not work on different systems. In that case, getting a distro (free distribution from online community) or installing certain command access via sudo (Super User) might help. Happy Linux-ing!
Version related Linux commands
Checking Version: cat simply displays the content of any file. Here, os-release file holds the Version data.
$ cat /etc/os-release NAME="Ubuntu" VERSION="20.04.2 LTS (Focal Fossa)" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 20.04.2 LTS" VERSION_ID="20.04" HOME_URL="https://www.ubuntu.com/" SUPPORT_URL="https://help.ubuntu.com/" BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/" PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy" VERSION_CODENAME=focal UBUNTU_CODENAME=focal
Network / Internet related Linux commands
Fetching server detail online: Tells server name of your website. curl is cURL You are piping (|) the command output into a command line utility called grep which filters out given pattern (‘erver’) for you and prints entire line. (server: nginx). GREP stands for Global Regular Expression Print. Regular Expression ‘erver’ works better because sometimes it fetches “S” of Server and not small “s”. We don’t want command to fail in any circumstances.
$ curl -Is https://wordpress.com | grep 'erver' server: nginx $ curl -I -s https://janiplastics.com | grep 'erver' server: Apache $ curl -sI https://lansdalelibrary.org | grep 'erver' Server: Apache/2.4.41 (Ubuntu)
Checking connectivity: Pinging the nodes to check the network connectivity. Press Ctrl + C to stop pinging & break the cycle.
$ ping 127.0.0.1 PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data. 64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.040 ms 64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.043 ms 64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.033 ms 64 bytes from 127.0.0.1: icmp_seq=4 ttl=64 time=0.041 ms 64 bytes from 127.0.0.1: icmp_seq=5 ttl=64 time=0.042 ms 64 bytes from 127.0.0.1: icmp_seq=6 ttl=64 time=0.042 ms 64 bytes from 127.0.0.1: icmp_seq=7 ttl=64 time=0.044 ms 64 bytes from 127.0.0.1: icmp_seq=8 ttl=64 time=0.043 ms ^C --- 127.0.0.1 ping statistics --- 8 packets transmitted, 8 received, 0% packet loss, time 7155ms rtt min/avg/max/mdev = 0.033/0.041/0.044/0.003 ms $ ping 127.0.1.1 PING 127.0.1.1 (127.0.1.1) 56(84) bytes of data. 64 bytes from 127.0.1.1: icmp_seq=1 ttl=64 time=0.040 ms 64 bytes from 127.0.1.1: icmp_seq=2 ttl=64 time=0.043 ms 64 bytes from 127.0.1.1: icmp_seq=3 ttl=64 time=0.045 ms 64 bytes from 127.0.1.1: icmp_seq=4 ttl=64 time=0.042 ms ^C --- 127.0.1.1 ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3071ms rtt min/avg/max/mdev = 0.040/0.042/0.045/0.002 ms
Website Record: Gives you entire record of any website including who is registrar, what is expiry date, what was creation date, etc…
$ whois janisoftwares.in Domain Name: janisoftwares.in Registry Domain ID: D414400000006614793-IN Registrar WHOIS Server: Registrar URL: www.godaddy.com Updated Date: 2020-08-09T15:37:43Z Creation Date: 2018-09-03T18:27:07Z Registry Expiry Date: 2025-09-03T18:27:07Z Registrar: GoDaddy.com, LLC ...... ...... ......
File related Linux commands
Getting file size data : Lists bytes, characters, lines, max line length, words (and the total in the end) of all the files present in the current working directory.
$ wc -cmlLw * 0 0 0 0 0 myCurl 3 12 57 57 30 myCurl.sh 3 12 57 57 30 total
Environment related Linux commands
$ env SHELL=/bin/bash SESSION_MANAGER=local/MATRIX:@/tmp/.ICE-unix/1420,unix/MATRIX:/tmp/.ICE-unix/1420 QT_ACCESSIBILITY=1 COLORTERM=truecolor XDG_CONFIG_DIRS=/etc/xdg/xdg-ubuntu-wayland:/etc/xdg SSH_AGENT_LAUNCHER=gnome-keyring XDG_MENU_PREFIX=gnome- GNOME_DESKTOP_SESSION_ID=this-is-deprecated LANGUAGE=en_AU:en LC_ADDRESS=en_IN GNOME_SHELL_SESSION_MODE=ubuntu LC_NAME=en_IN SSH_AUTH_SOCK=/run/user/1000/keyring/ssh XMODIFIERS=@im=ibus DESKTOP_SESSION=ubuntu-wayland LC_MONETARY=en_IN GTK_MODULES=gail:atk-bridge PWD=/home/neo LOGNAME=neo XDG_SESSION_DESKTOP=ubuntu-wayland XDG_SESSION_TYPE=wayland XAUTHORITY=/run/user/1000/.mutter-Xwaylandauth.DDRQ70 GJS_DEBUG_TOPICS=JS ERROR;JS LOG HOME=/home/neo USERNAME=neo IM_CONFIG_PHASE=1 LC_PAPER=en_IN LANG=en_AU.UTF-8 LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.zst=01;31:*.tzst=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.wim=01;31:*.swm=01;31:*.dwm=01;31:*.esd=01;31:*.jpg=01;35:*.jpeg=01;35:*.mjpg=01;35:*.mjpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36: XDG_CURRENT_DESKTOP=ubuntu:GNOME VTE_VERSION=6003 WAYLAND_DISPLAY=wayland-0 GNOME_TERMINAL_SCREEN=/org/gnome/Terminal/screen/972cc580_3b7b_488b_81d3_bb68f7b0d078 INVOCATION_ID=2c9c583f0b394a2485290ec02f1879bc MANAGERPID=1277 GJS_DEBUG_OUTPUT=stderr GNOME_SETUP_DISPLAY=:1 LESSCLOSE=/usr/bin/lesspipe %s %s XDG_SESSION_CLASS=user TERM=xterm-256color LC_IDENTIFICATION=en_IN LESSOPEN=| /usr/bin/lesspipe %s USER=neo GNOME_TERMINAL_SERVICE=:1.115 DISPLAY=:0 SHLVL=1 LC_TELEPHONE=en_IN QT_IM_MODULE=ibus LC_MEASUREMENT=en_IN PAPERSIZE=a4 XDG_RUNTIME_DIR=/run/user/1000 LC_TIME=en_IN JOURNAL_STREAM=8:38059 XDG_DATA_DIRS=/usr/share/ubuntu-wayland:/usr/local/share/:/usr/share/:/var/lib/snapd/desktop PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin GDMSESSION=ubuntu-wayland DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus LC_NUMERIC=en_IN _=/usr/bin/env
Super User (sudo) related Administrative Linux commands
Installing the Commands: You often get to see other Linux users accessing some commands which are not there on your Terminal. How to install those? Below is htop Command installed using “sudo snap install”. The sudo is Super User Do. It gives you access for installing new Commands.
$ htop Command 'htop' not found, but can be installed with: sudo snap install htop # version 3.0.5, or sudo apt install htop # version 2.2.0-2build1 See 'snap info htop' for additional versions. $ sudo snap install htop [sudo] password for neo: htop 3.0.5 from Maximiliano Bertacchini (maxiberta) installed
Update the Packages: the above (sudo snap install) is not about installing packages. For handling (installing / updating / upgrading / uninstalling) packages we use commands of apt (Advanced Packaging Tool). REMEMBER: You must update before upgrade. So here is the update command of apt. It synchronizes the package index files from source. Updates the list of available packages.
IF YOU RUN WITHOUT sudo PERMISSION, YOU GET OUTPUT SOMETHING LIKE THIS. $ apt-get update Reading package lists... Done E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied) E: Unable to lock directory /var/lib/apt/lists/ W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (13: Permission denied) W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (13: Permission denied) SO LET'S RUN USING sudo AND SEE THE DIFFERENCE FOR YOURSELF. sudo apt-get update [sudo] password for neo: Hit:1 http://in.archive.ubuntu.com/ubuntu focal InRelease Hit:2 http://in.archive.ubuntu.com/ubuntu focal-updates InRelease Hit:3 http://in.archive.ubuntu.com/ubuntu focal-backports InRelease Get:4 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB] Get:5 http://security.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [27.6 kB] Get:6 http://security.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [60.7 kB] Get:7 http://security.ubuntu.com/ubuntu focal-security/multiverse amd64 DEP-11 Metadata [2,468 B] Fetched 205 kB in 3s (67.7 kB/s) Reading package lists... Done
Dependency Verification: Check the packages for broken dependencies.
$ sudo apt-get check [sudo] password for neo: Reading package lists... Done Building dependency tree Reading state information... Done
Cleaning up old archives: We often keep on downloading new things without realizing how much old junk we have accumulated that is unused. Following command helps you rrases old downloaded archive files.
$ sudo apt-get autoclean Reading package lists... Done Building dependency tree Reading state information... Done Del systemd-timesyncd 245.4-4ubuntu3.7 [28.1 kB] Del systemd 245.4-4ubuntu3.7 [3,806 kB] Del libudev1 245.4-4ubuntu3.7 [77.6 kB] Del ubuntu-release-upgrader-gtk 1:20.04.33 [9,360 B] Del udev 245.4-4ubuntu3.7 [1,366 kB] Del ubuntu-release-upgrader-core 1:20.04.33 [23.8 kB] Del systemd-sysv 245.4-4ubuntu3.7 [10.3 kB] Del libsystemd0 245.4-4ubuntu3.7 [270 kB] Del libpam-systemd 245.4-4ubuntu3.7 [186 kB] Del ubuntu-advantage-tools 27.1~20.04.1 [837 kB] Del python3-distupgrade 1:20.04.33 [104 kB] Del libnss-systemd 245.4-4ubuntu3.7 [96.1 kB]
Process related Linux commands
Process Status:
$ ps
PID TTY TIME CMD
6799 pts/2 00:00:00 bash
8870 pts/2 00:00:00 ps
Linux Task Manager: This command is like Task Manager in MS-Windows. Shows all current ongoing processes with Process IDs, Priorities, User Names, Memory status, CPU usage, etc…
$ top
Interactive Task Manager on Linux: htop provides you an User Interface for viewing, sorting, searching and killing the processes. You can directly send the status code to the process from here. e.g. Select a process, Press F9 to kill it.
$ htop
Memory related Linux commands
Expert’s advice: Though it is possible to carry out fine tunning of RAM (e.g. defragment). Copying huge data on RAM and put it on SWAP and then defragment. However, it is not a good idea because the data duplication or redundancy may be shared by other applications. Defragmentation removes those and this can make your system unstable.
In fact, Unix like systems such as Linux never requires a patch-up utility like Defragment. Microsoft gave that to fix its own error [as per some experts].
RAM on your Linux: How much memory is free, how much is used up.
$ cat /proc/meminfo MemTotal: 4027472 kB MemFree: 1051932 kB MemAvailable: 2246136 kB Buffers: 71540 kB Cached: 1333848 kB SwapCached: 0 kB Active: 530428 kB Inactive: 2104344 kB Active(anon): 1968 kB Inactive(anon): 1275516 kB Active(file): 528460 kB Inactive(file): 828828 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 2097148 kB SwapFree: 2097148 kB Dirty: 272 kB Writeback: 0 kB AnonPages: 1229372 kB Mapped: 454188 kB Shmem: 48104 kB KReclaimable: 83680 kB Slab: 146508 kB SReclaimable: 83680 kB SUnreclaim: 62828 kB KernelStack: 9920 kB PageTables: 19868 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 4110884 kB Committed_AS: 4770612 kB VmallocTotal: 34359738367 kB VmallocUsed: 25052 kB VmallocChunk: 0 kB Percpu: 3056 kB HardwareCorrupted: 0 kB AnonHugePages: 0 kB ShmemHugePages: 0 kB ShmemPmdMapped: 0 kB FileHugePages: 0 kB FilePmdMapped: 0 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Hugetlb: 0 kB DirectMap4k: 194304 kB DirectMap2M: 3999744 kB
IN BYTES $ free total used free shared buff/cache available Mem: 4029484 1780392 460692 42208 1788400 1948380 Swap: 2097148 33080 2064068 IN GIGA BYTES (HUMAN READABLE). $ free -h total used free shared buff/cache available Mem: 3.8Gi 1.8Gi 354Mi 39Mi 1.7Gi 1.8Gi Swap: 2.0Gi 32Mi 2.0Gi
Statistical Reports on Virtual Memory with various outputs due to various options.
THE SWAP MEMORY STATUS CAN BE SEEN HERE.
$ vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
2 0 599312 139036 24204 452632 2 15 61 57 160 539 15 4 79 1 0
SLAB WISE INFO.
$ vmstat -s
4029484 K total memory
3467948 K used memory
2925428 K active memory
618996 K inactive memory
180836 K free memory
21816 K buffer memory
358884 K swap cache
2097148 K total swap
604472 K used swap
1492676 K free swap
660315 non-nice user cpu ticks
1112 nice user cpu ticks
186259 system cpu ticks
3432216 idle cpu ticks
55684 IO-wait cpu ticks
0 IRQ cpu ticks
1364 softirq cpu ticks
0 stolen cpu ticks
2629086 pages paged in
2487977 pages paged out
25440 pages swapped in
168083 pages swapped out
94131691 interrupts
197966757 CPU context switches
1627633057 boot time
8209 forks
SUMMARY OF THE (HARD) DISK STATISTICS.
$ vmstat -D
20 disks
3 partitions
91471 total reads
34330 merged reads
5260882 read sectors
752765 milli reading
84432 writes
254299 merged writes
4989210 written sectors
342946 milli writing
0 inprogress IO
812 milli spent IO
SECTOR WISE DISK STATISTICS.
~$ vmstat -d
disk- ------------reads------------ ------------writes----------- -----IO------
total merged sectors ms total merged sectors ms cur sec
loop0 54 0 2188 7747 0 0 0 0 0 5
loop1 65 0 2200 15377 0 0 0 0 0 5
loop2 59 0 2140 12733 0 0 0 0 0 5
loop3 69 0 2912 13228 0 0 0 0 0 5
loop4 45 0 708 5316 0 0 0 0 0 4
loop5 451 0 14566 7255 0 0 0 0 0 7
loop6 47 0 718 3811 0 0 0 0 0 2
loop7 521 0 16986 7272 0 0 0 0 0 6
sda 84246 34381 5043130 614670 84631 254535 4996658 343936 0 722
loop8 137 0 8692 3725 0 0 0 0 0 3
loop9 41 0 280 3835 0 0 0 0 0 3
loop10 55 0 2180 5756 0 0 0 0 0 4
loop11 1090 0 26562 9948 0 0 0 0 0 8
loop12 59 0 2146 10984 0 0 0 0 0 3
loop13 1968 0 14500 7512 0 0 0 0 0 5
loop14 45 0 716 4110 0 0 0 0 0 3
loop15 1137 0 26850 6025 0 0 0 0 0 7
loop16 45 0 710 3155 0 0 0 0 0 2
loop17 1306 0 89780 10405 0 0 0 0 0 14
loop18 132 0 4130 307 0 0 0 0 0 0
External device / source related Linux commands.
Everything in Linux is file. Linux has its own file system. File system starts with root “/”. Various items are mounted in various respective folders. e.g. system functions are mounted on /sys. Processes are mounted on /proc, so on and so forth. To see a list of everything mounted, just run “mount” command on command prompt.
$ mount sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime) proc on /proc type proc (rw,nosuid,nodev,noexec,relatime) udev on /dev type devtmpfs (rw,nosuid,noexec,relatime,size=1984112k,nr_inodes=496028,mode=755,inode64) devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000) tmpfs on /run type tmpfs (rw,nosuid,nodev,noexec,relatime,size=402748k,mode=755,inode64) /dev/sda5 on / type ext4 (rw,relatime,errors=remount-ro) securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime) tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,inode64) tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k,inode64) tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755,inode64) cgroup2 on /sys/fs/cgroup/unified type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate) cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,name=systemd) pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime) none on /sys/fs/bpf type bpf (rw,nosuid,nodev,noexec,relatime,mode=700) cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset) cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct) cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices) cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer) cgroup on /sys/fs/cgroup/pids type cgroup (rw,nosuid,nodev,noexec,relatime,pids) cgroup on /sys/fs/cgroup/rdma type cgroup (rw,nosuid,nodev,noexec,relatime,rdma) cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event) cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio) cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls,net_prio) cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb) cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory) systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=28,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=16626) debugfs on /sys/kernel/debug type debugfs (rw,nosuid,nodev,noexec,relatime) tracefs on /sys/kernel/tracing type tracefs (rw,nosuid,nodev,noexec,relatime) mqueue on /dev/mqueue type mqueue (rw,nosuid,nodev,noexec,relatime) hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,pagesize=2M) fusectl on /sys/fs/fuse/connections type fusectl (rw,nosuid,nodev,noexec,relatime) configfs on /sys/kernel/config type configfs (rw,nosuid,nodev,noexec,relatime) /var/lib/snapd/snaps/android-studio_113.snap on /snap/android-studio/113 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/atom_279.snap on /snap/atom/279 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/android-studio_114.snap on /snap/android-studio/114 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/atom_282.snap on /snap/atom/282 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/core_11420.snap on /snap/core/11420 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/core18_2066.snap on /snap/core18/2066 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/core18_2074.snap on /snap/core18/2074 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/core20_1081.snap on /snap/core20/1081 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/core20_1026.snap on /snap/core20/1026 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/curl_47.snap on /snap/curl/47 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/curl_233.snap on /snap/curl/233 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/gnome-3-34-1804_66.snap on /snap/gnome-3-34-1804/66 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/gnome-3-34-1804_72.snap on /snap/gnome-3-34-1804/72 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/gtk-common-themes_1515.snap on /snap/gtk-common-themes/1515 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/gtk-common-themes_1514.snap on /snap/gtk-common-themes/1514 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/htop_2802.snap on /snap/htop/2802 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/intellij-idea-ultimate_311.snap on /snap/intellij-idea-ultimate/311 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/snap-store_518.snap on /snap/snap-store/518 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/snap-store_547.snap on /snap/snap-store/547 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/snapd_12398.snap on /snap/snapd/12398 type squashfs (ro,nodev,relatime,x-gdu.hide) /var/lib/snapd/snaps/snapd_12704.snap on /snap/snapd/12704 type squashfs (ro,nodev,relatime,x-gdu.hide) /dev/sda1 on /boot/efi type vfat (rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro) tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=402744k,mode=700,uid=1000,gid=1000,inode64) gvfsd-fuse on /run/user/1000/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000) /dev/fuse on /run/user/1000/doc type fuse (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000) tmpfs on /run/snapd/ns type tmpfs (rw,nosuid,nodev,noexec,relatime,size=402748k,mode=755,inode64) nsfs on /run/snapd/ns/snap-store.mnt type nsfs (rw)
Mount / Unmount: When some external source / devices (such as Pen Drive / Flash drive / External Hard Drive) needs to be accessed by Linux, that source’s file system essentially has to be attached at a particular point (specified directory) in the file system of Linux. Once done, the Linux operating system’s Kernel is instructed about path, label and uuid of this source the device’s files and folders are available and ready to use. The CLI command $ mount attaches, whereas $ umount detaches. Ubuntu VERSION=”20.04.2 LTS (Focal Fossa)” has automatic detection of external HDD. Run $ mount CLI command before and after to see the difference. You will find additional file system mounted in the end.
LISTS ALL FILE SYSTEMS MOUNTED SO FAR. (BEFORE CONNECTING EXTERNAL HDD). $ mount -l sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime) proc on /proc type proc (rw,nosuid,nodev,noexec,relatime) udev on /dev type devtmpfs (rw,nosuid,noexec,relatime,size=1984120k,nr_inodes=496030,mode=755,inode64) ... ... ... tmpfs on /run/snapd/ns type tmpfs (rw,nosuid,nodev,noexec,relatime,size=402748k,mode=755,inode64) nsfs on /run/snapd/ns/snap-store.mnt type nsfs (rw) LISTS ALL FILE SYSTEMS MOUNTED SO FAR. (AFTER CONNECTING EXTERNAL HDD). $ mount -l sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime) proc on /proc type proc (rw,nosuid,nodev,noexec,relatime) udev on /dev type devtmpfs (rw,nosuid,noexec,relatime,size=1984120k,nr_inodes=496030,mode=755,inode64) ... ... ... tmpfs on /run/snapd/ns type tmpfs (rw,nosuid,nodev,noexec,relatime,size=402748k,mode=755,inode64) nsfs on /run/snapd/ns/snap-store.mnt type nsfs (rw) /dev/sdb1 on /media/neo/ANUP JANI type fuseblk (rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other,blksize=4096,uhelper=udisks2) [ANUP JANI]
Though Ubuntu 20.04.2 offers auto detection feature of external HDD, some might recommend to unmount it to ensure secure unplugging of external HDD, however the umount command is very dangerous (umount -a removes all file systems from disk) I woul simply unplug without umount.
It’s your call.
VERY HELPFUL COMMAND AND COMMAND OPTION.
$ help
$ <Any #Linux CLI command> --help
Jani Softwares 
