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1500 questions
60
votes
7 answers

What is swap memory?

I am using RAM for storing some of my database tables and the others are stored in hard disk. Today I came to know that my processes are using swap memory. Now what is swap memory and how can I detect that which process is using swap memory and how…
developer
60
votes
18 answers

Favorite rsync tips and tricks

The more I use rsync the more I realise that it's a swiss army knife of file transfer. There are so many options. I recently found out that you can go --remove-source-files and it'll delete a file from the source when it's been copied, which makes…
Amandasaurus
  • 33,461
60
votes
8 answers

What does "TTL expired in transit" mean on a ping attempt?

We get the message “TTL expired in transit” when we try to ping to a server in a different network segment. When we run tracert, 4 ip addresses repeat themselves indefinitely: 14 60 ms 59 ms 60 ms xxx.xxx.xxx.2 15 83 ms 81 ms 82…
Leonardo
  • 705
60
votes
6 answers

Ending company IT Admin relationship

We have been using a company to administer our (small office) IT infrastructure. We don't have complete records of what has been done or hasn't been done and don't know what we need to ask for in order to pick this up ourselves. Is there a good…
albiglan
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60
votes
7 answers

How do I know I'm running inside a linux "screen" or not?

The "screen" refers to a program mentioned in How to reconnect to a disconnected ssh session . That is a good facility. But there is a question I'd really like to know. How do I know whether I'm running inside a "screen"? The difference is: If…
Jimm Chen
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  • 32
60
votes
5 answers

What is the first digit for in 4-digit octal Unix file permission notation?

3-digit: 644 ugo (user group other) 4-digit: 0644 ?ugo (??? user group other) What is the first octal digit for in 4-digit octal Unix file permission notation?
Steven T. Snyder
  • 1,163
60
votes
8 answers

Why would I need a firewall if my server is well configured?

I admin a handful of cloud-based (VPS) servers for the company I work for. The servers are minimal ubuntu installs that run bits of LAMP stacks / inbound data collection (rsync). The data is large but not personal, financial or anything like that…
Aitch
  • 1,169
60
votes
2 answers

Are EC2 security group changes effective immediately for running instances?

I have an EC2 instance running, and it belongs to a security group. If I add a new allowed connection to that security group through AWS Management Console, should that change be effective immediately? Or perhaps only after restart of the…
Jonik
  • 3,121
60
votes
6 answers

shutdown: What is difference between "Power Off" and "Halt"?

With your typical Linux shutdown command, what is the difference between halting the system and powering off the system?
Jake Wilson
  • 9,133
60
votes
6 answers

How do I print contents of at jobs?

I have a Debian box with some jobs scheduled using at. I know I can list the jobs with their times using atq, but is there any way to print out their contents, apart from peeking into /var/spool/cron/atjobs?
che
  • 749
60
votes
4 answers

Linux command line character limit

I'm passing a variable to a script on the command line. What is the character limit of a command? eg: $ MyScript reallyreallyreally...reallyreallyreallylongoption Thanks.
robdog
  • 703
60
votes
7 answers

Is it okay to use a SSH key with an empty passphrase?

When I first learned how to make ssh keys, the tutorials I read all stated that a good passphrase should be chosen. But recently, when setting up a daemon process that needs to ssh to another machine, I discovered that the only way (it seems) to…
mozillalives
  • 1,073
59
votes
6 answers

How to backup GPG?

What are the critical files I need to backup from GPG? I guess my private key would qualify of course, but what else?
jldupont
  • 1,989
59
votes
6 answers

How to allow a user to use journalctl to see user-specific systemd service logs?

I am running user-level services in Ubuntu 16.04 LTS. For example, I have my test.service located at ~/.config/systemd/user/test.service. I was able to run the service by doing systemctl --user start test.target However, when I try to read its log…
ChromeHearts
  • 710
59
votes
1 answer

Can't enter the letter 'e' over ssh

Right now I am experiencing some very, very weird behaviour on a Ubuntu 14.04.2 LTS server I am managing. Connecting to the server over ssh either from cygwin(mintty) or a terminal on a Linux machine, I can't type the letter e. I have done the…
Zulakis
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