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K Dhanesh
K Dhanesh

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Practise the Linux Basic Commands

#linux #devops

Unix Tools

Bash Commands 

uname -a ## Get the Kernel Version lsb_release -a # Release or Distibution info cat /etc/SuSE-release # Suse Linux Version Check cat /etc/debian_version # Debian Version check
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Basic Commands to know the Server status 

uptime # it will shows how long the system has been running hostname # System Host Name hostname -i # To Display to the ip address of the Host, Linux based distribution man hier # File system hierarchy Description last reboot # to know the system reboot history
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Hardware informations

Kernel Detected HW 

dmesg # Detect Hardware and Boot messages lsdev # Info about the installed Hardware like PCI Card dd if=/dev/mem bs=1k skip=768 count=256 2>/dev/null | strings -n 8 # Read BIOS
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Linux 

cat /proc/cpuinfo # CPU Model cat /proc/meminfo # Hardware Memory grep MemTotal /proc/meminfo # Physical Memory watch -n1 'cat /proc/interrupts' # watch changecable interrupts free -m # To know the used & free memory ( -m for MB) cat /proc/devices # Configured devices lspci -tv # PCI Device info lsusb -tv # USB Device info lshal # List all devices with properties dmidecode # DMI/SMBIOS: hw info from the BIOS
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Free BSD 

sysctl hw.model # CPU Model sysctl hw # More information about hardware sysctl hw.ncpu # No. of active CPU's Installed sysctl vm # Memory Usage sysctl hw.realmem # Hardware Memory (Physical) sysctl -a | grep mem # Kernel memory settings and info sysctl dev # Configured devices pciconf -l -cv # PCI Device info usbdevs -v # USB Device info atacontrol list # ATA Device info camcontrol devlist -v # SCSI Device info
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Load, Statistics and Messages

Folowing Commands are useful to find out what is going on the system realtime.

top # display & update the top CPU processes mpstat 1 # display processors related statistics vmstat 2 # virtual memory statistics iostat 2 # I/O statistics - 2sec intervals systat -vmstat 1 # system statistics - 1sec intervals systat -tcp 1 # tcp connections (try also -ip) systat -netstat 1 # active network connections - BSD systat -ifstat 1 # network traffic through active interfaces - BSD systat -iostat 1 # CPU and Disk throughput - BSD ipcs -a # info on system V interprocess tail -n 500 /var/log/messages # Last 500 Kernel/syslog messages tail /var/log/warn # System Warnings messages see syslog.conf
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Users 

id # To display the active user ID with login & group last # To know the last logins on the server who or w # Who is logged on the server currently in simple type "w" groupadd admin # Adding group "admin" useradd -c "Dhanesh Kumar" -g admin -m colin # Creating user "Dhanesh Kumar", with "admin" group usermod -a -G <group> <user> # Adding existing user to the group - Debian Based groupmod -A <user> <group> # Adding existing user to the group - Suse Linux userdel dhanesh # delete the user "dhanesh" (linux / Solaris) adduser dhanesh # FreeBSD add user joe (interactive) rmuser dhanesh # FreeBSD delete user joe (interactive) pw groupadd admin # Use pw on FreeBSD pw groupmod admin -m newmember # Add a new member to a group pw useradd dhanesh -c "Dhanesh Kumar" -g admin -m -s /bin/tcsh pw userdel dhanesh; pw groupdel admin
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/etc/shadow - Encrypted passwords are stored

Temporarily prevent system logings for all user except ROOT user, with nologin.

echo "Apologies no login now" > /etc/nologin #(linux) echo "Apologies no login now" > /var/run/nologin #(FreeBSD)
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Limits in Linux

Some application requires higer limits on open files and sockets (like a proxy web server, database). The default limits are usually too low.

Shell/Script

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