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1500 questions
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votes
6 answers

Which PHP (opcode) cache one should use and why?

I keep hearing about some PHP (opcode) caches like - APC, XCache, Memcache, eAccelerator, etc. But I couldn't ever figure out how to go about choosing one. Apart from performance benefit, which a caching system is supposed to deliver, which other…
rahul286
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4 answers

Fingerprint of PEM ssh key

I have a PEM file which I add to a running ssh-agent: $ file query.pem query.pem: PEM RSA private key $ ssh-add ./query.pem Identity added: ./query.pem (./query.pem) $ ssh-add -l | grep query 2048 ef:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX…
Unknown
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43
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9 answers

sshd service fails to start

I'm not sure why it isn't starting or why its preventing me from connecting, i get this error: sshd.service - OpenSSH Daemon Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled) Active: failed (Result: start-limit) since Wed…
aCoolBean
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43
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1 answer

Is there still a use for irqbalance on modern hardware?

This question has been asked before, but I believe that the world has changed enough for it to be asked again. Does irqbalance have any use on today’s systems where we have NUMA-capable CPUs with memory sharing between their cores? Running…
espenfjo
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43
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8 answers

What is the value of JAVA_HOME for CentOS?

I have install java through yum on CentOS, however another java programme needs to know what the JAVA_HOME environmental variable is. I know all about setting environmental variables, but what do I set it to? java is installed in /usr/bin/java, it…
Amandasaurus
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43
votes
5 answers

Intentionally cause an I/O error in Linux?

Is there anyway, with Linux, to purposely cause a block device to report an I/O error, or possibly simulate one for testing purposes?
Dok
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43
votes
4 answers

Is there a way to list all configurable `alternatives` (symlinks for similar commands) on the system?

The alternatives command (package chkconfig) on RHEL/Fedora manages symlinks which link a generic name to one of the alternative implementations. For example, mta group of symlinks can be provided by Sendmail and Postfix (to implement i.e. sendmail…
uvsmtid
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43
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1 answer

Why does `tar -xvfz` fail, but `tar xvfz` work?

tar -xvfz foo.tar.gz returns an error tar: z: Cannot open: No such file or directory This is completely understandable - the f switch expects a filename, and so needs to be last. However, omitting the hyphen tar xvfz foot.tar.gz works and…
anu
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43
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2 answers

Should I use IPv6 only or both IPv4 and IPv6 in my web server?

My web server (Ubuntu, Nginx) have both IPv4 and IPv6 addresses assigned by the host. For my website, shall I bind it to only an IPv6 address? Is it the standard recommended way? Or, shall I use both IPv4 and IPv6 addresses?
THpubs
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43
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5 answers

User per virtual host in Nginx

Is it possible in nginx configure different user per virtual host? Something like server { user myprojectuser myprojectgroup; ... }
Alex Netkachov
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43
votes
5 answers

Why does DNS work the way it does?

This is a Canonical Question about DNS (Domain Name Service). If my understanding of the DNS system is correct, the .com registry holds a table that maps domains (www.example.com) to DNS servers. What is the advantage? Why not map directly to an…
sabof
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43
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1 answer

EC2: is an instance's public DNS stable? Can I rely on it not changing?

I've launched my first instance, and am using it as a web server. I see that it has a public DNS (a public URL), e.g.: ec2-123-45-6-789.compute-1.amazonaws.com I can successfully go to this server in my browser, hit it via cURL, etc. I want to use…
Aseem Kishore
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43
votes
1 answer

Curl POST - 411 Length Required

We have a RestFUL API we build in PHP. If we make the request: curl -u api-key:api-passphrase https://api.domain.com/v1/product -X POST We get back: 411 - Length Required Though if we simply add -d "" onto the request it works and no 411 error. Is…
Justin
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1 answer

How do I tell what is running on which ports in Ubuntu?

How could I tell what is listening on which ports on Ubuntu? In other words, how do I get a list of ports that are in use?
Genadinik
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5 answers

Why use Kerberos instead of NTLM in IIS?

This is something that I've never really been able to answer as well as I like: What is the real advantage of using Kerberos authentication in IIS instead of NTLM? I've seen a lot of people really struggle to get it set up (myself included) and I…
Infotekka
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