System Information
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uname -a
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Display Linux system information
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uname -r
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Display kernel release information
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cat /etc/redhat-release
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Show which version of redhat installed
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uptime
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Show how long the system has been running + load
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hostname
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Show system host name
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hostname -I
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Display the IP addresses of the host
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last reboot
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Show system reboot history
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date
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Show the current date and time
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cal
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Show this month's calendar
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w
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Display who is online
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whoami
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Who you are logged in as
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Performance Monitoring and Statistics
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top
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Display and manage the top processes
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htop
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Interactive process viewer (top alternative)
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mpstat 1
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Display processor related statistics
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vmstat 1
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Display virtual memory statistics
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iostat 1
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Display I/O statistics
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tail 100 /var/log/messages
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Display the last 100 syslog messages (Use
/var/log/syslog for Debian based systems.)
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tcpdump -i eth0
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Capture and display all packets on interface eth0
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tcpdump -i eth0 'port 80'
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Monitor all traffic on port 80 (HTTP)
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lsof
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List all open files on the system
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lsof -u user
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List files opened by user
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watch df -h
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showing periodic updates
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User Information and Management
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Id
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Display the user and group ids of your current user
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last
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Display the last users who have logged onto the system
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who
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Show who is logged into the system
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w
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Show who is logged in and what they are doing
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groupadd test
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Create a group named "test"
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useradd -c "Subhash" -m subhash
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Create an account named subhash, with a comment of "Subhash" and create the user's home directory
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userdel subhash
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Delete the subhash account
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usermod -aG it subhash
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Add the subhash account to the it group
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Files and Directory Commands
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ls -al
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List all files in a long listing (detailed) format
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pwd
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Display the present working directory
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mkdir directory
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Create a directory
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rm file
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Remove (delete) file
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rm -r directory
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Remove the directory and its contents recursively
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rm -f file
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Force removal of file without prompting for confirmation
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rm -rf directory
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Forcefully remove directory recursively
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cp file1 file2
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Copy file1 to file2
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cp -r source_directory destination
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Copy source directory recursively to destination. If destination exists, copy source directory into destination, otherwise create destination with the contents of source directory.
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mv file1 file2
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Rename or move file1 to file2. If file2 is an existing directory, move file1 into directory file2
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ln -s /path/to/file linkname
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Create symbolic link to linkname
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touch file
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Create an empty file or update the access and modification times of file
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cat file
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View the contents of file
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less file
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Browse through a text file
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head file
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Display the first 10 lines of file
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tail file
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Display the last 10 lines of file
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tail -f file
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Display the last 10 lines of file and "follow" the file as it grows
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Process Management
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ps
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Display your currently running processes
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ps -ef
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Display all the currently running processes on the system
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ps -ef | grep processname
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Display process information for processname
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top
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Display and manage the top processes
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htop
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Interactive process viewer (top alternative)
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kill pid
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Kill process with process ID of pid
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killall processname
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Kill all processes named processname
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program &
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Start program in the background
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bg
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Display stopped or background jobs
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fg
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Brings the most recent background job to foreground
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fg n
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Brings job n to the foreground
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Networking
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ifconfig -a
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Display all network interfaces and ip address
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ifconfig eth0
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Display eth0 address and details
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ethtool eth0
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Query or control network driver and hardware settings
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ping host
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Send ICMP echo request to host
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whois domain
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Display whois information for domain
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dig domain
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Display DNS information for domain
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dig -x IP_ADDRESS
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Reverse lookup of IP_ADDRESS
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host domain
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Display DNS ip address for domain
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hostname -i
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Display the network address of the hostname
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hostname -I
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Display all local ip addresses
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Download http://domain.com/file
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netstat -nutlp
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Display listening tcp and udp ports and corresponding programs
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Archives
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tar cf archive.tar directory
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Create tar named archive.tar containing directory
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tar xf archive.tar
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Extract the contents from archive.tar
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tar czf archive.tar.gz directory
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Create a gzip compressed tar file name archive.tar.gz
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tar xzf archive.tar.gz
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Extract a gzip compressed tar file
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tar cjf archive.tar.bz2 directory
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Create a tar file with bzip2 compression
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tar xjf archive.tar.bz2
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Extract a bzip2 compressed tar file
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Installing Packages
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yum search keyword
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Search for a package by keyword
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yum install package
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Install package
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yum info package
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Display description and summary information about package
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rpm -i package.rpm
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Install package from local file named package.rpm
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yum remove package
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Remove/uninstall package
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Search
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grep pattern file
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Search for pattern in file
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grep -r pattern directory
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Search recursively for pattern in directory
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locate name
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Find files and directories by name
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find /home/john -name 'prefix*'
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Find files in /home/john that start with "prefix"
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find /home -size +100M
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Find files larger than 100MB in /home
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SSH
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ssh host
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Connect to host as your local username
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ssh user@host
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Connect to host as user
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ssh -p port user@host
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Connect to host using port
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File Transfer
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scp file.txt server:/tmp
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Secure copy file.txt to the /tmp folder on server
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scp server:/var/www/*.html /tmp
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Copy *.html files from server to the local /tmp folder
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scp -r server:/var/www /tmp
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Copy all files and directories recursively from server to the current system's /tmp folder
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rsync -a /home /backups/
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Synchronize /home to /backups/home
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rsync -avz /home server:/backups/
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Synchronize files/directories between the local and remote system with compression enabled
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Hardware Information
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dmesg
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Display messages in kernel ring buffer
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cat /proc/cpuinfo
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Display CPU information
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cat /proc/meminfo
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Display memory information
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free -h
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Display free and used memory (-h for human readable, -m for MB, -g for GB.)
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lspci -tv
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Display PCI devices
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lsusb -tv
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Display USB devices
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dmidecode
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Display DMI/SMBIOS (hardware info) from the BIOS
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hdparm -i /dev/sda
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Show info about disk sda
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hdparm -tT /dev/sda
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Perform a read speed test on disk sda
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badblocks -s /dev/sda
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Test for unreadable blocks on disk sda
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Disk Usage
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df -h
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Show free and used space on mounted filesystems
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df -i
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Show free and used inodes on mounted filesystems
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fdisk -l
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Display disks partitions sizes and types
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du -ah
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Display disk usage for all files and directories in human readable format
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du -sh
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Display total disk usage off the current directory
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Directory Navigation
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cd ..
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To go up one level of the directory tree. (Change into the parent directory.)
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cd
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Go to the $HOME directory
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cd /opt
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Change to the /opt directory
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