Sunday, August 17, 2014

Linux Commands For A Beginner [Updated]

These are a few Linux commands for a beginner or a newbie. This may help out someone who is trying to quickly learn some basic commands in Linux world. All the best!!!



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PurposeCommands
View/List Files/Folders“ls” OR “ll”

“ls -ali” (view all including hidden files)

“ls -ld” (view only folders)

“ls -Zl” (view SELinux context along with file attributes)
Copy Files/Folders“cp” {cp <Options> <Source> <Destination>}
Secure Copy“scp” {scp <User@Host:SourcePath> <User@Host:DestinationPath>}

- Check manual page of scp for further options.
Move Files/Folders“mv” {mv <Options> <Source> <Destination>}
Create a New File“touch <Filename>” {creates an empty file}
OR
“vim <Filename> {allows editing new file}
Create a Directory“mkdir <DirectoryName>”
OR
“mkdir -p <PathOfTheDirectory>” {this would create all the directories/sub-directories in the given path if not available}
View a File“cat”

# cat <FileName>
Change Directory“cd <DirectoryName>” {directory name could be an absolute path}

“cd -" {to switch to the previous directory}

“cd ~” {to go to user home directory}

“cd ..” {to go back to parent directory OR scroll up in the directory list}
Print Current Working Directory“pwd”
Delete a File/Folder“rm <File/FolderName>”

“rm -rf <File/FolderName>” {this would wipe out a file/folder and doesn’t prompt for confirmation}
Check File Type“file” {file <File/FolderName> }
Change File/Folder Permissions“chmod”
Ex:# chmod o+w /testfile (sets write permission for this file for other users)

OR
# chmod 646 /testfile
Change File/Folder Ownership“chown”

Ex:# chown redhat /testfile (changes file owner as redhat user)

Ex:# chown redhat:redhat /testfile (changes owner and group to redhat user for this file)
View File Special Attributes"lsattr"
Set File Special Attributes“chattr”

Ex:#chattr +i /testfile (this would not allow file deletion even by root user)

#chattr -i /testfile (this removes “immutable flag” set on the file)
View ACL attributes
(Access Control List)
“getfacl <File/FolderName>”
Set ACL attributes
(Access Control List)
“setfacl -m u:<Username>:<Permissions> <File/FolderPath>”

Ex: # setfacl -m u:testuser:rw /etc/fstab
Check Kernel Version“uname” {# uname -a Or # uname -r}
Check Red Hat Release Version# cat /etc/redhat-release

OR
# cat /etc/os-release
Check OS Architecture# arch

Or

# uname -m
List of PCI Devices Found# lspci
List of USB Devices Found# lsusb
List of Hard Drives Found“fdisk” {# fdisk -l}

OR
“parted” {# parted --list}
Get Processors Details“lscpu”
OR
# cat /proc/cpuinfo
OR
# dmidecode --type processor
Get Memory Modules Details# dmidecode --type memory
List HAL Devices Found# lshal
List Block Devices Found“lsblk”

# lsblk -f (this would show up block devices along with file system)
List Swap Device# swapon -s

OR
# cat /proc/swaps
Check RAM(Random Access Memory)“free” {# free -m Or # free -g = display in Megabytes/Gigabytes format}

OR
# cat /proc/meminfo
List Modules Loaded# lsmod
List Mounted Devices“mount” (# mount)
OR
# cat /proc/mounts
OR
# cat /etc/mtab
OR
“df” (# df -h)
Check File System Usage# df -Th
Check/Display Hostname
# hostname

# hostname -f {this would show-up the Fully Qualified Domain Name}
OR
# sysctl -n kernel.hostname

# cat /etc/hostname { in RHEL7 }

Check System Uptime# uptime
Check SELinux Status
(Security Enhanced Linux)

# sestatus
OR
# cat /etc/sysconfig/selinux

# cat /etc/selinux/config { in RHEL7 }

Find The IP Address
“ifconfig” {# ifconfig -a}
OR
# ip a

Find Current User Logged-in# who -s

OR
# whoami
Check Current Date & Time# date
Switch User“su”
Shutdown Command# shutdown -h now

OR
# poweroff

OR
# halt

OR
# init 0

# systemctl poweroff { in RHEL7 }

Reboot Command# shutdown -r now

OR
# reboot

OR
# init 6

# systemctl reboot { in RHEL7 & above }

Check Current Runlevel
# runlevel

OR
# who -r

# systemctl get-default { in RHEL7 and above }

Switch from Runlevel 3 (text mode) to Runlevel 5 (GUI Mode)

{ In RHEL7, it is targets not runlevel }
#init 5

OR
#startx

# systemctl set-default graphical.target { in RHEL7 }
# systemctl isolate graphical.target

Switch from Runlevel 5 to Runlevel 3
# init 3

# systemctl set-default multi-user.target { in RHEL7 }
# systemctl isolate multi-user.target

Create a Partition on a Hard DriveUsing “fdisk” or “parted” command
Create ext4 File System# mkfs.ext4 <DeviceName>

OR
# mke2fs -t ext4 <DeviceName>
Create ext3 File System# mkfs.ext3 <DeviceName>

OR
# mke2fs -t ext3 <DeviceName>

Check File System for Errors {recommended to un-mount file system before running this command}

#e2fsck -f -y <DeviceName> {-f =force, -y =set automatic answer Yes}
Check if Network Interface is Up {I’ve taken first network interface “eth0” into reference here}# ping localhost

OR
# ethtool eth0 {check for “Link Detected”}

OR
# ifconfig eth0 {check for “UP” in the fourth line}

OR
# ip addr show eth0 {in RHEL7 and above }

OR
# ip a s eth0

List out Running Processes# ps aux

OR
# ps -ef

OR
# top
Search for a file# locate <FileName>

# find <PathWhereToSearch> -name <FileName> -type f

Ex:# find / -name hello.txt -type f {this would search for the file “hello.txt” under the / (root) directory}
Search for a word in a file“grep”

# grep -i <Word> <FileName> {this would search for the “word” within “FileName” regardless of case}
View top 10 lines in a file“head”

# head <FileName>
View bottom 10 lines in a file“tail”

# tail <FileName>
Check All the Daemons/Services Running# service --status-all

# systemctl list-units --type service --all { in RHEL7 }
List Services Started in
Run-level 5

#chkconfig --list |grep “5:on”

# chkconfig --list {This would list out all the services/daemons running and their status in each run level}

# chkconfig --list |grep “3:on” {this would list out all the services which are running on run-level 3}

# systemctl list-units --type service  { in RHEL7 }


NOTE: These are a few basic commands commonly used, there would be a many alternatives available, to get complete syntax help check out the “man” pages of a command.

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