How to Install GUI In CentOS 7

1) yum groupinstall  "GNOME Desktop" -Y
2) systemctl get-default
3) systemctl set-default graphical.target
4) systemctl get-default
5) systemctl isolate graphysical.target

Regards
Gurudatta N.R

How to delete a file which is throwing operation not permitted) from root acount.

Unable to delete file in Linux/Unix, operation not permitted) from root account.

chattr -i -a filename 

chmod ugo+w  filename 

rm filename

Regards

Gurudatta N.R 

How to Install and Configure VNC on Centos 6

In order to access the GUI of our linux servers

1) yum install tigervnc-server xterm

# vncpasswd

# vi /etc/sysconfig/vncservers

      VNCSERVERS="2:root"

      VNCSERVERARGS[2]="-geometry 1024x768"

# service vncserver start

# chkconfig vncserver on

Regards

Gurudatta N.R

How to list the users in Linux.

awk -F":" '{print "Login:" $1 "\tName:" $5 "\tHome:" $6}' /etc/passwd

Regards

Gurudatta N.R 

How to install the Grub in Linux .

Boot the server using the Linux CD and Type "linux rescue" on the boot prompt.

Once you get the Shell Prompt, Now follow the steps:

# chroot /mnt/sysimage

Now issue the command "grub-install "

 

For Example:

    

# grub-install /dev/sda

Now the grub will be reinstalled in the primary hard disk.

Regards

Gurudatta N.R

Linux Signals

Signal Name	Number	Description
SIGHUP	1	Hangup (POSIX)
SIGINT	2	Terminal interrupt (ANSI)
SIGQUIT	3	Terminal quit (POSIX)
SIGILL	4	Illegal instruction (ANSI)
SIGTRAP	5	Trace trap (POSIX)
SIGIOT	6	IOT Trap (4.2 BSD)
SIGBUS	7	BUS error (4.2 BSD)
SIGFPE	8	Floating point exception (ANSI)
SIGKILL	9	Kill(can't be caught or ignored) (POSIX)
SIGUSR1	10	User defined signal 1 (POSIX)
SIGSEGV	11	Invalid memory segment access (ANSI)
SIGUSR2	12	User defined signal 2 (POSIX)
SIGPIPE	13	Write on a pipe with no reader, Broken pipe (POSIX)
SIGALRM	14	Alarm clock (POSIX)
SIGTERM	15	Termination (ANSI)
SIGSTKFLT	16	Stack fault
SIGCHLD	17	Child process has stopped or exited, changed (POSIX)
SIGCONT	18	Continue executing, if stopped (POSIX)
SIGSTOP	19	Stop executing(can't be caught or ignored) (POSIX)
SIGTSTP	20	Terminal stop signal (POSIX)
SIGTTIN	21	Background process trying to read, from TTY (POSIX)
SIGTTOU	22	Background process trying to write, to TTY (POSIX)
SIGURG	23	Urgent condition on socket (4.2 BSD)
SIGXCPU	24	CPU limit exceeded (4.2 BSD)
SIGXFSZ	25	File size limit exceeded (4.2 BSD)
SIGVTALRM	26	Virtual alarm clock (4.2 BSD)
SIGPROF	27	Profiling alarm clock (4.2 BSD)
SIGWINCH	28	Window size change (4.3 BSD, Sun)
SIGIO	29	I/O now possible (4.2 BSD)
SIGPWR	30	Power failure restart (System V)

Linux crash-analyze The one tutorial that has it all

https://www.dedoimedo.com/computers/crash-analyze.html

How to get the serial number of the disk in Linux .

#!/bin/bash
#    NAME
#      getSerial.sh - Get HDD/SDD serial number

echo ""
echo "Device name and Serial Number"
filename="/tmp/devices"
lsblk |grep disk | awk '{print $1}' > $filename
sed -i -e 's/^/\/dev\//' $filename

while read -r device
do
  serial=$(smartctl -i $device |grep Serial)
  printf '%s - %s\n' "$device" "$serial"
done < $filename
# -------------------------------------------------------------------
# EndOfFile
# -------------------------------------------------------------------

.

How to find the PCI device information in Linux. ?

We can find the PCI device using the following methods.

1)   vendors by name 

2)   vendors by id 

3)   search devices

http://pcidatabase.com/vendor_details.php?id=607

The Linux kernel represents PCI devices as pseudo-devices in the sysfs file system:

$ ls -la /sys/bus/pci/devices
total 0
drwxr-xr-x 2 root root 0 2009-08-03 10:38 .
drwxr-xr-x 5 root root 0 2009-08-03 10:38 ..
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:00.0 -> ../../../devices/pci0000:00/0000:00:00.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:01.0 -> ../../../devices/pci0000:00/0000:00:01.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:01.1 -> ../../../devices/pci0000:00/0000:00:01.1
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:02.0 -> ../../../devices/pci0000:00/0000:00:02.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:02.1 -> ../../../devices/pci0000:00/0000:00:02.1
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:04.0 -> ../../../devices/pci0000:00/0000:00:04.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:05.0 -> ../../../devices/pci0000:00/0000:00:05.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:05.1 -> ../../../devices/pci0000:00/0000:00:05.1
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:05.2 -> ../../../devices/pci0000:00/0000:00:05.2
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:06.0 -> ../../../devices/pci0000:00/0000:00:06.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:0a.0 -> ../../../devices/pci0000:00/0000:00:0a.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:0b.0 -> ../../../devices/pci0000:00/0000:00:0b.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:0c.0 -> ../../../devices/pci0000:00/0000:00:0c.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:0d.0 -> ../../../devices/pci0000:00/0000:00:0d.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:0e.0 -> ../../../devices/pci0000:00/0000:00:0e.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:0f.0 -> ../../../devices/pci0000:00/0000:00:0f.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:18.0 -> ../../../devices/pci0000:00/0000:00:18.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:18.1 -> ../../../devices/pci0000:00/0000:00:18.1
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:18.2 -> ../../../devices/pci0000:00/0000:00:18.2
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:00:18.3 -> ../../../devices/pci0000:00/0000:00:18.3
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:01:05.0 -> ../../../devices/pci0000:00/0000:00:06.0/0000:01:05.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:01:06.0 -> ../../../devices/pci0000:00/0000:00:06.0/0000:01:06.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:02:00.0 -> ../../../devices/pci0000:00/0000:00:0a.0/0000:02:00.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:03:00.0 -> ../../../devices/pci0000:00/0000:00:0a.0/0000:02:00.0/0000:03:00.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:03:00.1 -> ../../../devices/pci0000:00/0000:00:0a.0/0000:02:00.0/0000:03:00.1
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:04:00.0 -> ../../../devices/pci0000:00/0000:00:0b.0/0000:04:00.0
lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:05:00.0 -> ../../../devices/pci0000:00/0000:00:0c.0/0000:05:00.0

Given an entry such as:

lrwxrwxrwx 1 root root 0 2009-08-03 10:38 0000:04:00.0 -> ../../../devices/pci0000:00/0000:00:0b.0/0000:04:00.0

We can break the device string "0000:04:00.0" down as follows:

0000 : PCI domain (each domain can contain up to 256 PCI buses)
04   : the bus number the device is attached to
00   : the device number
.0   : PCI device function

To get additional information about the device, we can change into the 0000:04:00.0 directory and execute our favorite pager to display one or more pseudo-device entries:

$ cd 0000:04:00.0

$ ls -la
total 0
drwxr-xr-x 4 root root     0 2009-08-03 10:38 .
drwxr-xr-x 7 root root     0 2009-08-03 10:38 ..
-rw-r--r-- 1 root root  4096 2009-08-03 12:23 broken_parity_status
-r--r--r-- 1 root root  4096 2009-08-03 10:38 class
-rw-r--r-- 1 root root  4096 2009-08-03 11:34 config
-r--r--r-- 1 root root  4096 2009-08-03 10:38 device
lrwxrwxrwx 1 root root     0 2009-08-03 10:38 driver -> ../../../../bus/pci/drivers/tg3
-rw------- 1 root root  4096 2009-08-03 12:23 enable
lrwxrwxrwx 1 root root     0 2009-08-03 12:12 firmware_node -> ../../../LNXSYSTM:00/device:00/PNP0A03:00/device:1a/device:1b
-r--r--r-- 1 root root  4096 2009-08-03 10:38 irq
-r--r--r-- 1 root root  4096 2009-08-03 12:23 local_cpulist
-r--r--r-- 1 root root  4096 2009-08-03 10:38 local_cpus
-r--r--r-- 1 root root  4096 2009-08-03 12:23 modalias
-rw-r--r-- 1 root root  4096 2009-08-03 12:23 msi_bus
drwxr-xr-x 3 root root     0 2009-08-03 10:38 net
-r--r--r-- 1 root root  4096 2009-08-03 12:23 numa_node
drwxr-xr-x 2 root root     0 2009-08-03 12:12 power
-r--r--r-- 1 root root  4096 2009-08-03 11:34 resource
-rw------- 1 root root 65536 2009-08-03 12:23 resource0
lrwxrwxrwx 1 root root     0 2009-08-03 10:38 subsystem -> ../../../../bus/pci
-r--r--r-- 1 root root  4096 2009-08-03 10:38 subsystem_device
-r--r--r-- 1 root root  4096 2009-08-03 10:38 subsystem_vendor
-rw-r--r-- 1 root root  4096 2009-08-03 10:38 uevent
-r--r--r-- 1 root root  4096 2009-08-03 10:38 vendor
-rw------- 1 root root 32768 2009-08-03 12:23 vpd

$ cat vendor
0x14e4

$ cat device
0x1659

$ cat class
0x020000

Each sysfs entry contains a unique piece of data, such as the PCI vendor id (vendor) the device class (class), the device identifier (device), and information on irq and resource assignments. In the next section, we will see how to decode this data

Note: Taken from the net. 

Regards

Gurudatta N.R

Linux well known port numbers

20 – FTP Data (For transferring FTP data)

21 – FTP Control (For starting FTP connection)

22 – SSH(For secure remote administration which uses SSL to encrypt the transmission)

23 – Telnet (For insecure remote administration

25 – SMTP(Mail Transfer Agent for e-mail server such as SEND mail)

53 – DNS(Special service which uses both TCP and UDP)

67 – Bootp

68 – DHCP

69 – TFTP(Trivial file transfer protocol uses udp protocol for connection less transmission of data)
80 – HTTP/WWW(apache)

88 – Kerberos

110 – POP3(Mail delivery Agent)

123 – NTP(Network time protocol used for time syncing uses UDP protocol)

137 – NetBIOS(nmbd)

139 – SMB-Samba(smbd)

143 – IMAP

161 – SNMP(For network monitoring)

389 – LDAP(For centralized administration)

443 – HTTPS(HTTP+SSL for secure web access)

514 – Syslogd(udp port)

636 – ldaps(both tcp and udp)

873 – rsync

989 – FTPS-data

990 – FTPS

993 – IMAPS

1194 – openVPN

1812 – RADIUS

995 – POP3s

2049 – NFS(nfsd, rpc.nfsd, rpc, portmap)

2401 – CVS server

3306 – MySql

3690 – SVN

6000-6063-X11


Regards
Gurudatta N.R