This December 2019, i have passed the Linux Foundation Certified System (LFCS) Administrator exam. This exam is provided by Linux Foundation Organization. An organization to maintain the open source ecosistem by provide an event, training and certification.

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For more details, you can visit their site here. For the Lxcf exam, here.
Having prior experience in using Linux/Unix based OS is must. Especially understand how this Operating System works generally and how to use the command line. Most of the question/task in this exam is hands-on Linux command.

For the LFCS Exam, a score of 66% or above must be earned to pass. FAQ for Linux Foundation here.

The number of the question on this exam is slightly different from each person. Seems based on the question/task weight and scoring. In my case, i have about 65-70 question.

The question domain based on my exam is;
– User/group management
– Storage management
– File manipulation
– Other’s command
By the way we can chose 2 distribution for this exam, Cent-OS/Ubuntu.

For this exam, i used the bundle package exam + course with Black Friday coupon 😀 though. But, the course is only general course how the Linux working.



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P.

Postifx Command Cheatsheet

List of helpfull command that used to help me when maintaining Postfix mailserver.

Hemat Pangkal Kaya

Insignificant one

List mail queue and MAIL_ID’s, list mail queue


Check the postfix version

Get default value set on the postfix config

Get non default value set on the postfix config

Flush the mail queuw

Force to send the queue

Process all emails stuck in the queue

Read email from mail queue

Remove certain mail from mail queue

Remove all mail queue

Fast method to remove mail from queue

Remove all the deferred mail in queue

Sorting email with “from address” filter

Remove all email that sent to [email protected]

Remove all email sent from [email protected]

Remove all email sent from the dom.ain

Mail queue stats short

Number of emails in Mail queue

Fast count of emails in mail queue

Watch Log Live

Count and sort success pop3/imap logins

Count and sort success SMTP postfix logins. This is usefull when you want to track a compromised account.

Count and sort success SMTP postfix logins on exact date “May 18”

Analyze Postfix Logs

You may need to install the pflogsumm package first.

F.

Find the user having high Inode usage


We can find the inode usage (Number of files) owned by each user/directory, especially useful in VPS. Each VPS will have inode limits (the maximum number of files that can be created in that VPS)

For example If the inode usage is 100 % then we needs to find out which user/directory has owned the maximum number of files.

Run the following commands

In my case the user mailnull (the system user used by exim to store queued emails) owned maximum number of files as there were around 30000 emails in the mail queue. From the command output shown below the mailnull user has the inode usage of 89971.

After mailnull the next user who has owned maximum number of files is test17 (58163). Now need to find out which directory contains maximum number of files.

( This script will display
the directory/file and count the number of files inside that directory )

Here again public_html directory contains the maximum number of files.

Finally the directory x7 contains the maximum number of files (inodes).

Similarly by using this method we can find out which user/directory owns the maximum number of files in any linux server.

This command might be helpful to you in finding the folder using a great part of the inodes. It outputs the top 5 file system objects utilizing the most inodes in the current folder: