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1500 questions
201
votes
11 answers

"Add correct host key in known_hosts" / multiple ssh host keys per hostname?

Trying to ssh into a computer I control, I'm getting the familiar message: @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! …
Samuel Edwin Ward
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200
votes
6 answers

How do I view the details of a digital certificate .cer file?

I am using Windows and have been given a .cer file. How can I view the details of it?
yazz.com
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200
votes
8 answers

How to setup passwordless `sudo` on Linux?

How can passwordless sudo access be setup on either RHEL (Fedora, CentOS, etc) or Ubuntu distributions? (If it's the same across distros, that's even better!) Setting: personal and/or lab/training equipment with no concern for unauthorized access…
warren
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197
votes
3 answers

Meaning of the buffers/cache line in the output of free

Why does my server show total used free shared buffers cached Mem: 12286456 11715372 571084 0 81912 6545228 -/+ buffers/cache: 5088232 7198224 Swap: 24571408 54528 24516880 I have no idea on…
Muahmmad Zeeshan
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197
votes
3 answers

Possible to change email address in keypair?

I've created an RSA keypair that I used for SSH, and it includes my email address. (At the end of the public key.) I've now changed my email address. Is it possible to change the email address on the key, or is it part of the key and I would have to…
Ram Rachum
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196
votes
22 answers

Is it normal to get hundreds of break-in attempts per day?

I just checked my server's /var/log/auth.log and found that I'm getting over 500 failed password/break-in attempt notifications per day! My site is small, and its URL is obscure. Is this normal? Should I be taking any measures?
Kyle Cureau
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195
votes
6 answers

LVM dangers and caveats

I have recently started using LVM on some servers for hard drives larger than 1 TB. They're useful, expandable and quite easy to install. However, I could not find any data about the dangers and caveats of LVM. What are the downsides of using LVM?
Adam Matan
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195
votes
15 answers

How to reconnect to a disconnected ssh session

Is there a way to connect to an ssh session that was disconnected? We are having problems with our network connection to a remote site that we are working on separately; however, in the mean time we experience a large number of disconnects due to…
palehorse
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195
votes
1 answer

SSH use only my password, Ignore my ssh key, don't prompt me for a passphrase

This is a question regarding the OpenSSH client on Linux, MacOSX and FreeBSD. Normally, I log into systems using my SSH key. Occasionally, I want my SSH client to ignore my SSH key and use a password instead. If I 'ssh hostname', my client prompts…
Stefan Lasiewski
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193
votes
6 answers

How to cd into a directory with this name "-2" (starting with the hyphen)?

I have a directory named: -2 I want to cd into it but the cd complains: bash: cd: -2: invalid option With no success, I've tried: cd "-2" cd '-2' cd \-2 Any solution? Edit: no file browsers like mc, etc. available on the server.
user151851
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190
votes
1 answer

What is a challenge password?

I'm setting up SSL on an Ubuntu server. One of fields it asks for as part of setting up the CSR is a "challenge password". What is that? The default is blank. Do I need to enter one?
Will Martin
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189
votes
12 answers

Physically locating the server

I've got a CentOS server somewhere in the building; I can login into it remotely and VNC, etc. Now I've got to physically move it, and for that I need to physically locate the machine among the lookalikes around the office. What can I do remotely to…
Michael
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189
votes
6 answers

Nginx config reload without downtime

I use nginx as a reverse proxy. Whenever I update the config for it using sudo "cp -r #{nginx_config_path}* /etc/nginx/sites-enabled/" sudo "kill -s HUP `cat /var/run/nginx.pid`" I face a brief downtime. How can I avoid that?
Saurav Shah
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189
votes
3 answers

Difference between KVM and QEMU

I have been reading about KVM and Qemu for sometime. As of now I have a clear understanding of what they do. KVM supports hardware virtualization to provide near native performance to the Guest Operating sytems. On the other hand QEmu emulates the…
Abhishek Gupta
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188
votes
2 answers

What are the different widely used RAID levels and when should I consider them?

This is a Canonical Question about RAID levels. What are: the RAID levels typically used (including the RAID-Z family)? deployments are they commonly found in? benefits and pitfalls of each?
MDMarra
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