like Uptime,Users,Sudo,cmp,lsusb, lsmod,lsblk ,ifconfig interface up,ifconfig interface down,dd,lsop,bc,last reboot,Vim and Watch. Let us start with command uptime
Uptime
The command uptime will show you the how long system has been running, how many users currently logged on and system load averages.[root@faraz ~]# uptime 14:23:55 up 2:36, 3 users, load average: 0.05, 0.18, 0.12 [root@faraz ~]#
Users
This command will print the names of users currently logged in to current host. Here it is showing two times login fahmed users and one time root.[root@faraz ~]# users fahmed fahmed root [root@faraz ~]#
Sudo
This will execute the command as another user with privileges and allow the user to work as superuser as specified by a security policy. First you need to edit the visudo file and make an entry for user with privileges. In the section group wheel make entry for fahmed user (%fahmed ALL=(ALL) ALL)[root@faraz ~]# visudo ## Allows people in group wheel to run all commands %wheel ALL=(ALL) ALL %fahmed ALL=(ALL) ALLNow you are able to use commands with privileges and you have the rights to execute.
[fahmed@faraz ~]$ sudo systemctl start smb [fahmed@faraz ~]$So far we have been starting/stopping services start with root user but now here sudo user can also start/stop the service as well.
cmp
This command compare two files byte by byte and will display difference.Syntax cmp file1 file2
[fahmed@faraz ~]$ cmp newstring.file upload.txt newstring.file upload.txt differ: byte 1, line 1 [fahmed@faraz ~]$
lsusb
This command will list the usb devices. As you can see in below image I have connected my usb with Kingston technology.[fahmed@faraz ~]$ lsusb Bus 001 Device 002: ID 0951:16a3 Kingston Technology Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub [fahmed@faraz ~]$
lsmod
This command will show the status of module in the Linux Kernel.[fahmed@faraz ~]$ lsmod Module Size Used by bnep 19704 2 bluetooth 372944 5 bnep rfkill 26536 2 bluetooth fuse 87741 3 xt_CHECKSUM 12549 1 ipt_MASQUERADE 12678 3 nf_nat_masquerade_ipv4 13412 1 ipt_MASQUERADE tun 27141 1 ip6t_rpfilter 12546 1 ip6t_REJECT 12939 2 ipt_REJECT 12541 4 xt_conntrack 12760 18 ebtable_nat 12807 0 ebtable_broute 12731 0 bridge 119562 1 ebtable_broute stp 12976 1 bridge llc 14552 2 stp,bridge
lsblk
This command will lists the information about all available or specified block devices gather information from filesystem.[fahmed@faraz ~]$ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 15G 0 disk ├─sda1 8:1 0 500M 0 part /boot └─sda2 8:2 0 14.5G 0 part ├─centos-root 253:0 0 13G 0 lvm / └─centos-swap 253:1 0 1.5G 0 lvm [SWAP] sr0 11:0 1 1024M 0 rom [fahmed@faraz ~]$ lsblk -l NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 15G 0 disk sda1 8:1 0 500M 0 part /boot sda2 8:2 0 14.5G 0 part centos-root 253:0 0 13G 0 lvm / centos-swap 253:1 0 1.5G 0 lvm [SWAP] sr0 11:0 1 1024M 0 rom [fahmed@faraz ~]$
Enable an Interface
You can enable system’s interface up by defining the name of the interface with ifconfig command. In CentOS/RedHat 7 interface card name is enp0s3. Older version has eth0.Syntax ifconfig interface-name up
[fahmed@faraz ~]$ sudo ifconfig enp0s3 up [fahmed@faraz ~]$
Disable an Interface
You can also disable the interface card.Syntax ifconfig interface-name down
[fahmed@faraz ~]$ sudo ifconfig enp0s3 down [fahmed@faraz ~]$
dd
This command will copy a file, converts and formats data according to the operands. This command is mostly used to copy the iso image into usb device or other media devices through if= input file and of=output file.[root@faraz ~]# dd if=/dev/dvdrw of=/home/fahmed/Downloads/CentOS.isoBe careful when you are defining the name of device (dvd or usb etc)
lsop
This command will list all the information about opened file in a file system (Like regular file, library file, network related file etc). Here I am going to show first top ten opened file because of lots of files are opened there in backend.[root@faraz ~]# lsof | head -10 lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs Output information may be incomplete. COMMAND PID TID USER FD TYPE DEVICE SIZE/OFF NODE NAME systemd 1 root cwd DIR 253,0 4096 128 / systemd 1 root rtd DIR 253,0 4096 128 / systemd 1 root txt REG 253,0 1494056 51226345 /usr/lib/systemd/systemd systemd 1 root mem REG 253,0 20032 33730331 /usr/lib64/libuuid.so.1.3.0 systemd 1 root mem REG 253,0 252704 34397999 /usr/lib64/libblkid.so.1.1.0 systemd 1 root mem REG 253,0 90632 33730310 /usr/lib64/libz.so.1.2.7 systemd 1 root mem REG 253,0 19888 33870478 /usr/lib64/libattr.so.1.1.0 systemd 1 root mem REG 253,0 19520 33596345 /usr/lib64/libdl-2.17.so systemd 1 root mem REG 253,0 153192 33660599 /usr/lib64/liblzma.so.5.0.99 [root@faraz ~]#bc
This command is basically to calculate two variables in a CLI mode its work just like a calculator.
[root@faraz ~]# bc bc 1.06.95 Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc. This is free software with ABSOLUTELY NO WARRANTY. For details type `warranty'. 6+2 8 6*11 66Last reboot
This command will show the last reboot times or system reboots history.
[root@faraz ~]# last reboot reboot system boot 3.10.0-327.4.4.e Fri Mar 18 11:47 - 14:58 (03:10) reboot system boot 3.10.0-327.10.1. Tue Mar 15 22:40 - 14:58 (2+16:17) reboot system boot 3.10.0-327.4.4.e Tue Mar 15 16:39 - 16:51 (00:11) reboot system boot 3.10.0-327.4.4.e Tue Mar 15 00:59 - 01:24 (00:25) reboot system boot 3.10.0-327.4.4.e Tue Mar 15 00:05 - 00:54 (00:49) reboot system boot 3.10.0-327.10.1. Mon Mar 14 06:03 - 00:54 (18:50) reboot system boot 3.10.0-327.4.4.e Mon Mar 14 04:10 - 05:36 (01:25) reboot system boot 3.10.0-327.4.4.e Sun Mar 13 23:02 - 05:36 (06:33) reboot system boot 3.10.0-327.4.4.e Thu Mar 10 23:06 - 23:24 (00:18)Vim
You can open file with vi or vim but how can we open file with or go to that particular line. Here I am going to open file with particular line. Syntax vi +line-number file-name
[fahmed@faraz ~]$ vi +10 newstring.file
Watch
This command is to execute a program and watch the program output changing over time. By default its run on every 2 seconds. Its display output and errors in full screen. It is basically watching the program in continuous form with time interval. You can run multiple commands at a time inside the quotes.
[root@faraz ~]# watch -n 1 'ls -l; echo; df'
In this tutorial we have learnt 14 useful linux commands
like Uptime,Users,Sudo,cmp,lsusb, lsmod,lsblk ,ifconfig interface up,ifconfig interface down,dd,lsop,bc,last reboot,Vim and Watch. I hope you have enjoyed this tutorial and will see you in
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