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Showing posts from February, 2016

Suspended Jobs vs Running jobs in Linux

Background Job : A job which is running background in the same shell. You can use bg command to see any background jobs. Foreground job : A Job which is running in the same shell right before your eyes. Suspended Job : Its a stopped/pause job but you can resume their running. Let me explain with example very clealy virt00 # sleep 180 ^ Z zsh : suspended sleep 180 virt00 # jobs [ 1 ] + suspended sleep 180 virt00 # bg [ 1 ] + continued sleep 180 virt00 # fg [ 1 ] + running sleep 180 ^ Z zsh : suspended sleep 180 virt00 # jobs [ 1 ] + suspended sleep 180 virt00 # I have started a Job named  sleep 180  then I stopped with CTRL+Z . right now my job is in suspended mode. I see it by typing  jobs  command. Now I want to resume its running in background so I typed  bg command then it will move from suspended state to running state but in background it will run. now I typed command  fg  to bring it foreground , now job wont get stepped but it will

Deny SSH access to particular users

We all know SSH is very famous and the best service for remote access. Today I am going to tell you how to block or allow only particular users or group from SSH access. open sshd_config file as per your environment in Debian vim /etc/ssh/sshd_config Then add below line to enable access for only below users AllowUsers username1 username2 to deny access for only below users add a line as DenyUsers username1 username2 as in the same way AllowGroups group1 group2 and to deny groups DenyGroups group1 group2  But there is something very important you have to follow here. It is the order of mentioning. From manpage of SSH  The allow/deny directives are processed in the following order: DenyUsers , AllowUsers , DenyGroups , and finally AllowGroups . So first mention DenyUsers and then AllowUsers then only it will works and same for DenyGroups and AllowGroups Hope it helps.

How to see IOWAIT in Linux

Hello , You can use sar command. in Ubuntu you can install it with sudo apt-get install systat and enable data collecting sed -i 's/ENABLED="false"/ENABLED="true"/' /etc/default/sysstat start service with   /etc/init.d/sysstat start To see I/O latency type command as sar 1 1 that means it will give two responses with 1 sec as interval. Example : root@virt01:~# sar 1 3 Linux 3.19.0-42-generic (virt01.ubuntu.com)     13/02/16        _x86_64_        (1 CPU) 12:26:23        CPU     %user     %nice   %system   %iowait    %steal     %idle 12:26:24        all      0.00      0.00      0.00      0.00      0.00    100.00 12:26:25        all      0.00      0.00      0.99      0.00      0.00     99.01 12:26:26        all      2.02      0.00      0.00      0.00      0.00     97.98 Average:        all      0.67      0.00      0.33      0.00      0.00     99.00 root@virt01:~# Hope that helps.