A Technical I.T./DevOps Blog
Question
You have seen “<(” in Linux. What does it do?
Answer
A command encapsulated in parens and having the “<” symbol on the left is a way to do process substitution.
Here is an example:
diff <(hostname -f) <(date)
The diff command can compare the results of two different commands. To read more about process substitution,
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Continue reading “What Does the Less-than and Parentheses Syntax in Linux/Bash Signify?”
Problem scenario
You want passwords to rotate periodically for all users. You modified the /etc/login.defs file, and new users are inheriting the temporal rotational policies for passwords. How can pre-existing accounts be forced to periodically change their password?
Solution
Use this command for every password (but replace “jdoe” with the user you want to change and replace “30” with the number of days you want the password to last for before the user is forced to change it):
sudo chage -M 30 jdoe
# The user can still log in one more time after expiration. …
Continue reading “How Do You Get Passwords to Expire for Existing Users?”
Problem scenario
You are running Linux with a multi-core CPU and motherboard. You want to turn off simultaneous multithreading (because in some use cases the performance can improve or you are concerned about security). What should you do?
Possible Solution #1
If you want to be able to turn it back on without rebooting, you could have a crontab job run a script at reboot.
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Continue reading “How Do You Disable Hyperthreading in Linux?”
Problem scenario
Using Python, you want to parse a log file. You want to print out entries that have a datetime stamp that are within 24 hours of a given date.
The log file is in this format:
Sep 18 07:28:11 server1 sshd[29284]: Received disconnect from 115.52.17.109 port 46970:11: Bye Bye [preauth]
Sep 18 07:28:11 server1 sshd[29284]: Disconnected from 115.52.17.109 port 46970 [preauth]
Sep 18 07:28:11 server1 sshd[29282]: Failed password for root from 51.10.7.109 port 24844 ssh2
Sep 18 07:28:13 server1 sshd[29287]: pam_unix(sshd:auth): authentication failure; …
Continue reading “Using Python How Do You Print Log Entries for a Given Time Range?”
Problem scenario
There is no audio on your Linux system. The volume is not muted. In the control panel area for audio you see “Dummy …” for your sound device on your Linux system. What should you do?
Possible Solution
This assumes the hardware of the server, computer or laptop uses Intel.
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Continue reading “How Do You Get Audio to Work on Your Linux System?”
Problem scenario
You have heard the term “threadjacking” in different contexts. What does it mean?
Answer
The word “threadjack” can have different meanings. It can be a netiquette issue, a cybersecurity issue, or both.
Threadjacking can refer to the practice of responding to an email thread or website posting to change the topic. These type of threadjackings have no security implication.
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Continue reading “Is the Term “Threadjacking” a Netiquette or Cybersecurity Issue?”
Problem scenario
You try to install VirtualBox on a Linux server via the “Software” section of your GUI. It fails with an error message like this: “Unable to install VirtualBox as download failed … not (yet) available (404 Not Found)”
Solution
Run a command like one of the following depending on the type of Linux you have.
If you have a Debian distribution of Linux (such as Ubuntu or Mint): sudo apt -y update
If you have a Red Hat distribution of Linux (such as CentOS,
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Problem scenario
When you log into Windows, you have an application that starts up automatically. What do you do to disable applications from running automatically?
Solution
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Continue reading “How Do You Stop Applications from Popping Up at Start Up?”
Problem scenario
You received a PD0455 check engine light. How do you resolve it?
Possible solution
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Continue reading “If you get a PD0455 check engine light, how do you fix it?”
Question
You see “lnext” or “LNEXT”, and you want to know what it means. In the context of Linux, what does LNEXT refer to?
Answer
It is a special character in Linux that pertains to the terminal driver. It means “Literal next.” To invoke the literal next character (and bypass other interpretations), an operator would typr Control-V.
The answer above was taken from page 1296 and 1298 of The Linux Programming Interface.
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