How to use screen command in Linux

--> To open a new screen:

#screen -S "Screenname"
Eg.: 

#screen -S "testscreen"

--> To deattach the screen:

Cntrl+A then D   //it will run after detach also
--->    Ctrl-a followed by k: close the current windows (kill)

--> To list the screen:

screen -list

--> To reattach the screen:

screen -r ScreenID------- From screen -list



Example:

# screen -S "testscreen"   // create screen name testscreen
Agent pid 21981

Now we are running small test script in "testscreen".

#/test.sh >>data.txt &  //ran script test.sh to append hello and date/time in data.txt
[1] 4917

Cntrl+A then D   //it will detach

[detached]
# screen -list   //list currently running screen
There is a screen on:
        3015.testscreen (Detached)
1 Socket in /var/run/uscreens/S-alhatul.

Reattch screen using following command
screen -r ScreenID
#screen -r 3015   //reattach screen
Agent pid 21981

output of screen command

Output of test.sh
===data.txt ======

#cat data.txt
hello
Fri Aug 30 15:21:00 CEST 2019
hello
Fri Aug 30 15:21:02 CEST 2019
hello
Fri Aug 30 15:21:04 CEST 2019
hello

Ctrl-a followed by k:
It will terminate current screen session.

#screen -list
No Sockets found in /var/run/uscreens/S-alhatul.

Reduce XFS filesystem on Linux

Hello friend ,

today i am going to discuss on XFS file system Limitation and that limitation is Linux admin cant reduce XFS file system online. after knowing this limitation i am still thinking about what is that preventing XFS shrink ? also is there any alternative way we can reduce size of XFS file system.

Yes, we can reduce size of XFS , but for this downtime needed.

Step 1: Backup existing file system backup using "xfsdump" 

Step 2: Then umount XFS file system.

Step 3: Then remove LV .

Step 4: Create required size LV.

Step 5: Mount File system.

But here Linux admin require downtime.

.........

Copy pedbg zip file using SCP from HMC to NIM server.

How to copy pedbg file after pedbg file created on HMC

Pedbg collected using "hscpe" user.

#pedbg -r 

Above command will remove previous data

Now collect fresh pedbg logs using following command

#pedbg -q 4 -c

This will generate file in /dump with name like /dump/hmclogs.hmcabc.zip

Copy thes to remote NIM or AIX Lpar using SCP command.

Login to NIM , create folder in /TMP like "pedbglogs"

#cd /tmp

#mkdir pedbglogs

#cd pedbglogs

# scp hscpe@hmcIP:/dump/hmclogs.hmcabc.zip  .

Here . Means current directory on NIM server. (/tmp/pedbglogs)

** Make sure /tmp have enough space to hold this pedbg file.

Thanks !!!!!

AIX lpar not connecting ,ssh process issue troubleshoot

Got incident for AIX LPAR not connecting from outside using ssh.

To solve this issue followed following approach.

First did pre-check like tried to connect from AIX NIM server and CyberArk, so found that its not connecting from both NIM and CyberArk.

so finally decided to try from putty, that also failed.

so, decided to take console from HMC and took session. upon checking found that "ssh" process is in inoperative state. so tried to start that process but its not starting using following command. :(

#startstc -s sshd 

#refresh -s sshd

so decided to check which process is holding that port 22. checked this using lsof command

#lsof -i :22

this command showing process id where socket status is "closed_wait",

so decided that will go for kill that process.

killed that process by command #kill -9 PID

and started "sshd" process and finally it work.

AIX lpar we able access from cyberARK ,putty and NIM.

Finally we conclude that, ssh process was in "hung" state and sshd process refresh and stop, start also not worked, then finally after clearing PID associated with that process solve issue.

Thanks !!!!

AIX HACMP ,GPFS and veritas Cluster state check command

 AIX HACMP ,GPFS and veritas Cluster state check command

AIX HACMP resource group state check command

#clRGinfo

How to check cluster is in  stable state or not

#lssrc -ls clstrmgrES |grep -i state

if output is showing "ST_STABLE" ,then cluster is in stable state .

#lssrc -g cluster   // Show process status in cluster group

GPFS cluster information check command

#mmgetstate -aLs

following command will show information about gpfs cluster

#mmlscluster

Veritas Cluster state check command

#hastatus -summ

Thanks !!!!!

How to replace faulty disk on AIX VIO rootvg using DIAG HOT plug task

 How to replace faulty disk on AIX VIO rootvg using DIAG HOT plug task??

AIX admin can replace faulty hard drive using

"DIAG" procedure. here faulty disk must support 

hot swap operation.

Before replacement we need to do some pre-check,

1. IS this part of rootvg and its in mirror ?

Ans : if yes then ,identify that disk and unmirror 

that disk from rootvg using following command.

#umirrovg rootvg hdisk1

#reducevg rootvg hdisk1

2. Identify disk location using lscfg command

#lscfg -vpl hdisk1

3. make sure that disk is removed from rootvg.

Once all precheck done we can identify hdisk1 by following procdure,

PART I

DIAG--->Certify media Task---->Hot plug task--->scsi and scsi RAID hot plug RAID manager----->Identify disk

Select hdisk1 and make sure location and disk is current and press enter key.

Example . 

XXX.XXX.XX.P2-C9-D5    //disk location

once "Enter key pressed" LED will blink, which set disk to identify mode.

once disk identified, you can exit from this menu by pressing "enter" and come to previous menu by "ESC +3"

PART II

Next is Remove and replace hdisk1

===============================

DIAG--->Certify media Task---->Hot plug task--->scsi and scsi RAID hot plug RAID manager----->Identify disk-->Replace / Remove a Device Attached to An SCSI Hot Swap Enclosure Device

select hdisk1 and make sure location and disk is current and press enter key.

XXX.XXX.XX.P2-C9-D5 

now disk is ready for remove and replace.

now you can ask remote engineer to perform disk replacement.

PART III

Once disk replaced you need to detect that disk on AIX LPAR.

follow below procedure it will configure newly replaced disk on LPAR.

DIAG--->Certify media Task---->Hot plug task--->scsi and scsi RAID hot plug RAID manager-->Configure Added/Replaced Devices

identify new disk by lspv and lscfg command 

#lscfg -vpl hdisk    // it will have new serial number.

Thanks !!!!

How to Delete million of file in certain directory

How to Delete million of file in certain directory.

When administrator get request for deleting files which having large number, then simple "rm" command will not work. Solution to this problem is following command.

find . -type f -name "*.bak" -exec rm -i {} \;

Above command will find files with ".bak" extension and will delete them. IF administrator want to specify any specific path then he also specify that path like below.

find /backup -type f -name "*.bak" -exec rm -i {} \;