General Keywords to be remembered while entering into CentOS

CentOS is build from the Red hat Enterprise Distribution. which is more stable than any other Linux Distributions because of its package updates were not too often which makes this OS standout from the que. Core version of this OS is very convenient compared to GUI version to acts as Server.

Click on image to go to CentOS official site

uname:

Uname command is used to find the version of Linux and the OS Architecture x86 or x64 bit

[root@10 ~]# uname -a
Linux 10.0.2.15 3.10.0-327.el7.x86_64 #1 SMP Thu Nov 19 22:10:57 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

uname -a provides the all details of the OS.

[root@10 ~]# uname --help
Usage: uname [OPTION]...
Print certain system information.  With no OPTION, same as -s.

  -a, --all                print all information, in the following order,
                             except omit -p and -i if unknown:
  -s, --kernel-name        print the kernel name
  -n, --nodename           print the network node hostname
  -r, --kernel-release     print the kernel release
  -v, --kernel-version     print the kernel version
  -m, --machine            print the machine hardware name
  -p, --processor          print the processor type or "unknown"
  -i, --hardware-platform  print the hardware platform or "unknown"
  -o, --operating-system   print the operating system
      --help     display this help and exit
      --version  output version information and exit

GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
For complete documentation, run: info coreutils 'uname invocation'


uname --help for additional arguments

top:

Top command shows the list of process running in background.

[root@10 ~]# top
top - 08:44:45 up 10 min,  1 user,  load average: 0.00, 0.15, 0.19
Tasks:  85 total,   2 running,  83 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.3 us,  2.0 sy,  0.0 ni, 97.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :   500780 total,   162304 free,    84752 used,   253724 buff/cache
KiB Swap:  1048572 total,  1048572 free,        0 used.   367316 avail Mem

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
   22 root      20   0       0      0      0 S  1.7  0.0   0:08.83 kworker/0:1
 9824 root      20   0  148184   2028   1452 R  0.7  0.4   0:00.15 top
   11 root      20   0       0      0      0 R  0.3  0.0   0:00.62 rcuos/0
    1 root      20   0   46380   6772   4028 S  0.0  1.4   0:03.13 systemd
    2 root      20   0       0      0      0 S  0.0  0.0   0:00.00 kthreadd
    3 root      20   0       0      0      0 S  0.0  0.0   0:00.82 ksoftirqd/0
    5 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kworker/0:0H
    6 root      20   0       0      0      0 S  0.0  0.0   0:00.15 kworker/u2:0
    7 root      rt   0       0      0      0 S  0.0  0.0   0:00.00 migration/0
    8 root      20   0       0      0      0 S  0.0  0.0   0:00.00 rcu_bh
    9 root      20   0       0      0      0 S  0.0  0.0   0:00.00 rcuob/0
   10 root      20   0       0      0      0 S  0.0  0.0   0:02.54 rcu_sched
   12 root      rt   0       0      0      0 S  0.0  0.0   0:00.30 watchdog/0
   13 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 khelper
   14 root      20   0       0      0      0 S  0.0  0.0   0:00.00 kdevtmpfs
   15 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 netns
   16 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 perf
   17 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 writeback
   18 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kintegrityd
   19 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 bioset
   20 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kblockd
   21 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 md
   26 root      20   0       0      0      0 S  0.0  0.0   0:00.00 khungtaskd
   27 root      20   0       0      0      0 S  0.0  0.0   0:00.00 kswapd0
   28 root      25   5       0      0      0 S  0.0  0.0   0:00.00 ksmd
   29 root      20   0       0      0      0 S  0.0  0.0   0:00.00 fsnotify_mark
   30 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 crypto
   38 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kthrotld
   39 root      20   0       0      0      0 S  0.0  0.0   0:00.01 kworker/u2:1
   40 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kmpath_rdacd
   41 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kpsmoused
   42 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 ipv6_addrconf
   62 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 deferwq
   93 root      20   0       0      0      0 S  0.0  0.0   0:00.00 kauditd
  258 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 ata_sff
  261 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 events_power_ef
  276 root      20   0       0      0      0 S  0.0  0.0   0:00.00 scsi_eh_0

free:

Free command is used to check the Memory Status of the server including RAM and Swap memory.

[root@10 ~]# free -m
              total        used        free      shared  buff/cache   available
Mem:            489          84         150          14         254         356
Swap:          1023           0        1023

hostname:

Hostname command is to check the current server name

[root@10 ~]# hostname
10.0.2.15

ip addr:

This command is to view the IP Address assigned to the server.

[root@10 ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:86:d9:d7 brd ff:ff:ff:ff:ff:ff
    inet 192.168.43.128/24 brd 192.168.43.255 scope global dynamic enp0s3
       valid_lft 2806sec preferred_lft 2806sec
    inet6 fe80::a00:27ff:fe86:d9d7/64 scope link
       valid_lft forever preferred_lft forever

vi Editor:

vi editor is often used by most pros for file editing in core edition.

[root@10 ~]# vi /tmp/test.txt
test
~
~
~
~
~
~
~
"/tmp/test.txt" 1L, 5C

Commands to use:
:w        - Save the edit
:q        - Exit file
:q!       - Exit without saving changes
:wq or :x - Save and exit the changes

cat:

cat is used to print the data available inside a file

[root@10 ~]# cat /tmp/test.txt
test

[root@10 ~]# cat /etc/*release
CentOS Linux release 7.2.1511 (Core)
NAME="CentOS Linux"
VERSION="7 (Core)"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="7"
PRETTY_NAME="CentOS Linux 7 (Core)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:7"
HOME_URL="https://www.centos.org/"
BUG_REPORT_URL="https://bugs.centos.org/"

CENTOS_MANTISBT_PROJECT="CentOS-7"
CENTOS_MANTISBT_PROJECT_VERSION="7"
REDHAT_SUPPORT_PRODUCT="centos"
REDHAT_SUPPORT_PRODUCT_VERSION="7"

CentOS Linux release 7.2.1511 (Core)
CentOS Linux release 7.2.1511 (Core)

cat /etc/*release will print all possible files ends with name ‘release’ will be printed from the /etc/ directory

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You must have walked into this Blog site with some interest on Server Administration and How to manage a server from scratch. Every journey begins with the first step. I was stepped into the this profile 4 years back and worked on many challenging environment and everything i have learned not from any Institute, my interest in learning things makes this possible. I believe in knowledge not Experience and Certification.

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