Server Down issue / unable to ssh the server / server not responding to pings.
There are so many reasons for a hostname/ip is not pingable.
a few reasons are:
1. Software issue
2. Hardare issue
3. Network issue
4. Other issue
First we will ping the server and check whether server is responding to pings or not.
Command: ping hostname
Here, we can see packet drops, if 0% packet loss, then server is reachable/responding to pings.
If 100% packet loss then host is not reachable.
1.Network related issue : ( make sure our network is working fine)
Cause:
a. Network link down → check with DC ( Data center ) or Hardware team.
b. Network cables are loose or damaged → check with DC ( Data center ) team.
c. no connection exist between our system to remote system → Check with Network team
2. Due to software issue: Host might be completely down
Get the approval to reboot the host if it is not sshable/pingable.
Login to console and set the host to boot from disk.
You can monitor the boot logs to find out the cause
or once the host is up , check the /var/log/messages or dmesg logs to find root cause.
3. Due to hardware issue : Host might be completely down
get the approval to reboot the host if it is not sshable/pingable.
Login to console and set the host to boot from disk.
You can monitor the boot logs to find out the cause
or once the host is up , check the /var/log/messages or dmesg logs to find root cause.
if still the host is not up , then check with DC team to know investigate further on hardware issue.
4. Other reasons: Host might be in power off state
cause:
a.somebody manually powered off the host due to any maintenanace activity
b. Power supply unit (PSU) problem, fan or temperature issue so system might went down.
HOSTNAME=newname.example.com → Modify this name to new name.
:wq
Once the file is saved, you need to reboot the server OR restart the below services to reflect the new server name.
#service network restart
#service NetworkManager restart
done.
Now verify using hostname command.
How to check the server IP address.
#hostname -i
#ifconfig → here you can see ip address as inet addr against eth0 interface
#ip addr show
To get the IP adress of interfaces:
$sudo ifconfig|awk 'sub(/inet addr:/,"") {print $1}'
To get interfaces only:
$echo `ifconfig`|awk '{print $1}'
script to print the ip adress for the interface when interface is given as first parameter to the script
echo -e "enter interface: \c"
read a
c=`ifconfig|awk 'sub(/$a/,"") {print $1}'`
echo "IP address of $a is : $c"
To check which ports are listening to the host
# netstat -nlp
# netstat -an | grep -i <portnumber>
# lsof -i:<portnumber>
If command is throwing permission denied
then I will try the following commands
1. Check whther I'm running the command as a root user or normal user.
( if im a root user , it should work)
2. If I dont have root access, then atleast I will try with
sudo command
3.I will see the path of command
sudo command /bin -maxdepth 1 -type f
4. if it is a script then i will try with
chmod u+x program_name
5. I will check the permsission of command using
ls -l /bin/ping
if it shows
-rwSr-xr-x 1 root root 36892 date /bin/ping
here lower case S in permission indicates execute permission is not set to user
(suid concept)
How to recover or reset Root password in LINUX?
Steps:
1. Reboot the system , while the server shows Grub, click Esc (escape )
2. Select the kernel , press the "e" key to edit the entry
3. Select second line (the line starting with the word kernel)
4. Press the "e" key to edit kernel entry so that you can append single user mode
5. Just give space and type 1
6. Click ENTER key
7. Now press the b key to boot the Linux kernel into single user mode
8. At prompt type passwd command to reset password of root.
There are so many reasons for a hostname/ip is not pingable.
a few reasons are:
1. Software issue
2. Hardare issue
3. Network issue
4. Other issue
First we will ping the server and check whether server is responding to pings or not.
Command: ping hostname
Here, we can see packet drops, if 0% packet loss, then server is reachable/responding to pings.
If 100% packet loss then host is not reachable.
1.Network related issue : ( make sure our network is working fine)
Cause:
a. Network link down → check with DC ( Data center ) or Hardware team.
b. Network cables are loose or damaged → check with DC ( Data center ) team.
c. no connection exist between our system to remote system → Check with Network team
2. Due to software issue: Host might be completely down
Get the approval to reboot the host if it is not sshable/pingable.
Login to console and set the host to boot from disk.
You can monitor the boot logs to find out the cause
or once the host is up , check the /var/log/messages or dmesg logs to find root cause.
3. Due to hardware issue : Host might be completely down
get the approval to reboot the host if it is not sshable/pingable.
Login to console and set the host to boot from disk.
You can monitor the boot logs to find out the cause
or once the host is up , check the /var/log/messages or dmesg logs to find root cause.
if still the host is not up , then check with DC team to know investigate further on hardware issue.
4. Other reasons: Host might be in power off state
cause:
a.somebody manually powered off the host due to any maintenanace activity
b. Power supply unit (PSU) problem, fan or temperature issue so system might went down.
NOTE: If Reboot / hardware maintenance ( drive replacement / cable replacement etc., ) , get necessary approvals nd proceed.
To check hostname?
$hostname
To change hostname
edit /etc/sysconfig/networkTo check hostname?
$hostname
To change hostname
HOSTNAME=newname.example.com → Modify this name to new name.
:wq
Once the file is saved, you need to reboot the server OR restart the below services to reflect the new server name.
#service network restart
#service NetworkManager restart
done.
Now verify using hostname command.
#hostname -i
#ifconfig → here you can see ip address as inet addr against eth0 interface
#ip addr show
To get the IP adress of interfaces:
$sudo ifconfig|awk 'sub(/inet addr:/,"") {print $1}'
To get interfaces only:
$echo `ifconfig`|awk '{print $1}'
script to print the ip adress for the interface when interface is given as first parameter to the script
echo -e "enter interface: \c"
read a
c=`ifconfig|awk 'sub(/$a/,"") {print $1}'`
echo "IP address of $a is : $c"
To check which ports are listening to the host
# netstat -nlp
# netstat -an | grep -i <portnumber>
# lsof -i:<portnumber>
If command is throwing permission denied
then I will try the following commands
1. Check whther I'm running the command as a root user or normal user.
( if im a root user , it should work)
2. If I dont have root access, then atleast I will try with
sudo command
3.I will see the path of command
sudo command /bin -maxdepth 1 -type f
4. if it is a script then i will try with
chmod u+x program_name
5. I will check the permsission of command using
ls -l /bin/ping
if it shows
-rwSr-xr-x 1 root root 36892 date /bin/ping
here lower case S in permission indicates execute permission is not set to user
(suid concept)
How to recover or reset Root password in LINUX?
Steps:
1. Reboot the system , while the server shows Grub, click Esc (escape )
2. Select the kernel , press the "e" key to edit the entry
3. Select second line (the line starting with the word kernel)
4. Press the "e" key to edit kernel entry so that you can append single user mode
5. Just give space and type 1
6. Click ENTER key
7. Now press the b key to boot the Linux kernel into single user mode
8. At prompt type passwd command to reset password of root.
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