Sunday, August 17, 2014

Linux Commands For A Beginner

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 Redhat Release Version#cat /etc/redhat-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}
OR
#cat /proc/partitions
List of Processors Found“lscpu”
OR
#cat /proc/cpuinfo
OR
#dmidecode --type processor
List of Memory Modules Found#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
Check Modules Loaded#lsmod
Check Mounted Devices“mount” (#mount)
OR
#cat /proc/mounts
OR
#cat /etc/mtab
OR
“df” (#df -h)
Check File System Usage#df -Th
Check Hostname#hostname

#hostname -f {this would show-up the Fully Qualified Domain Name}
Check System Uptime#uptime
Check SELinux Status
(Security Enhanced Linux)
#sestatus
OR
#cat /etc/sysconfig/selinux
Find The IP Address“ifconfig” {#ifconfig -a}
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
Reboot Command#shutdown -r now
OR
#reboot
OR
#init 6
Check Current Runlevel#runlevel
OR
#who -r
Switch from Runlevel 3 (text mode) to Runlevel 5 (GUI Mode)#init 5
OR
#startx
Switch from Runlevel 5 to Runlevel 3#init 3
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}
Check 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
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}
*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.