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1500 questions
107
votes
5 answers

SSH keypair generation: RSA or DSA?

SSH supports two signature algorithms for key pairs: RSA and DSA. Which is preferred, if any? For RSA, what is the minimum acceptable key length?
Brad Ackerman
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107
votes
11 answers

Send Ctrl-Alt-Del to nested RDP session

Is there a way to send the Ctrl-Alt-Del command to an RDP session (Windows Server 2008 R2) inside another RDP session (also Windows Server 2008 R2) without the first session catching it? Ctrl+Alt+End and Ctrl+Alt+Shift+End do not reach the 2nd level…
xddsg
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107
votes
14 answers

Is Ping a reliable way to check if a server is available?

In my application I am pinging a server and waiting for a response. I am using this to determine whether the server is available and responsive or not. Is this a reliable way of determining availability? I assume a firewall could be filtering icmp…
Peter Kelly
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107
votes
6 answers

"POSSIBLE BREAK-IN ATTEMPT!" in /var/log/secure — what does this mean?

I've got a CentOS 5.x box running on a VPS platform. My VPS host misinterpreted a support inquiry I had about connectivity and effectively flushed some iptables rules. This resulted in ssh listening on the standard port and acknowledging port…
Mike B
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106
votes
16 answers

How do I find if there is a rogue DHCP server on my Network?

What's the best approach towards determining if I have a rogue DHCP server inside my network? I'm wondering how most admins approach these kinds of problems. I found DHCP Probe through searching, and thought about trying it out. Has anyone had…
l0c0b0x
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106
votes
5 answers

Best way to gracefully restart CentOS?

I always used the command: shutdown -r now However, sometimes that causes MySQL issues. What's the most graceful way to restart CentOS? I've seen: reboot and halt How can I gently reboot the machine?
User
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106
votes
2 answers

an upstream response is buffered to a temporary file

I have a rather large and slow (complex data, complex frontend) web application build in RoR and served by Puma with nginx as reverse proxy. Looking at the nginx error log, I see quite a few entries like: 2014/04/08 09:46:08 [warn] 20058#0: *819237…
ngw
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106
votes
2 answers

escaping double quotes and percent signs (%) in cron

The following command works from prompt but not from crontab. grep abc /var/log/messages | grep "`date '+%B %d'`" | mail -s"abc log of `hostname`" s.o+`hostname`@gmail.com I need to add it to daily cron.
shantanuo
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106
votes
6 answers

How to let 'cp' command don't fire an error when source file does not exist?

I'm using Mac OS X. I'm trying to copying some files with cp command for a build script like this. cp ./src/*/*.h ./aaa But this command fires an error if there is no .h file in ./src directory. How to make the command don't fire the error? (silent…
Eonil
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106
votes
8 answers

How to determine JAVA_HOME on Debian/Ubuntu?

On Ubuntu it is possible to have multiple JVMs at the same time. The default one is selected with update-alternatives. But this does not set the JAVA_HOME environment variable, due to a debian policy. I am writing a launcher script (bash), which…
Witek
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105
votes
3 answers

Is there a way to see the execution tree of systemd?

What I mean under the question is: is there a way to dump the ordered list (like pstree does for processes) to see how systemd executed the supplied set of units, i.e. the tree after the dependencies were resolved and jobs were queued for the…
galaxy
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105
votes
6 answers

Is X.Y.Z.0 a valid IP address?

Are IP addresses with a 0 in the last octet valid? 10.6.43.0 In my case, I have the the following netmask 255.255.252.0 What about a 0 for the other octets?
Alan H
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104
votes
1 answer

Differences and dis/advanages between: Fast-CGI, CGI, Mod-PHP, SuPHP, PHP-FPM

There are few different php "wrappers"(?). What are differences between them? Tried to google some, but cant seem to find informations. (mod-php is not googleable). Why might I choose one over another?
Gacek
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104
votes
10 answers

Properly setting up a "default" nginx server for https

I have several servers running on the same machine, some with http only, some with both http and https. There are several server blocks defined in separate files which are included from the main config file. I have set up a "default" server for…
Roar
104
votes
17 answers

CentOS vs. Ubuntu

I had a web server that ran Ubuntu, but the hard drive failed recently and everything was erased. I decided to try CentOS on the machine instead of Ubuntu, since it's based on Red Hat. That association meant a lot to me because Red Hat is a…
DLH
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