45
votes
5answers
9k views

Can you help me with my software licensing issue?

This is a Canonical Question about Licensing. Questions on licensing are off-topic on Server Fault. If your question has been closed as a duplicate of this question, then this is because we ...
307
votes
12answers
54k views

How do I deal with a compromised server?

This is a Canonical Question about Server Security - Responding to Breach Events (Hacking) See Also: Tips for Securing a LAMP Server Reinstall after a Root Compromise? Canonical ...
50
votes
2answers
7k views

Can you help me with my capacity planning?

This is a Canonical Question about Capacity Planning Related: How do you do Load Testing and Capacity Planning for Web Sites? How do you do Load Testing and Capacity Planning for ...
140
votes
5answers
19k views

Redirect, Change URLs or Redirect HTTP to HTTPS in Apache - Everything You Ever Wanted How to Know about Mod_Rewrite Rules but Were Afraid to Ask

This is a Canonical Question about Apache's mod_rewrite. Changing a request URL or redirecting users to a different URL than the one they originally requested is done using mod_rewrite. This ...
239
votes
5answers
51k views

How does IPv4 Subnetting Work?

This is a Canonical Question about IPv4 Subnets. Related: How does IPv6 subnetting work and how does it differ from IPv4 subnetting? How does Subnetting Work, and How do you do it ...
51
votes
3answers
9k views

How do you do load testing and capacity planning for web sites?

This is a canonical question about capacity planning for web sites. Related: Can you help me with my capacity planning? How do you do Load Testing and Capacity Planning for ...
45
votes
3answers
27k views

Why is my crontab not working, and how can I troubleshoot it?

This is a Canonical Question about using cron & crontab. The answer for 'Why is my crontab not working, and how can I troubleshoot it?' can be seen below. This addresses the cron system with ...
82
votes
1answer
4k views

I am under DDoS. What can I do?

This is a Canonical Question about DoS and DDoS mitigation. I found a massive traffic spike on a website that I host today; I am getting thousands of connections a second and I see I'm using all ...
104
votes
2answers
13k views

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? ...
25
votes
6answers
39k views

How to send emails and avoid them being classified as spam

This is a canonical question about how to handle email sent from your server being misclassified as spam. For additional information you may find these similar questions helpful: Best ...
86
votes
4answers
57k views

What permissions should my website files/folders have on a Linux webserver?

This is a Canonical Question about File Permissions on a Linux web server. I have a Linux web server running Apache2 that hosts several websites. Each website has its own folder in /var/www/. ...
25
votes
3answers
2k views

Why is Linux reporting “free” memory strangely?

This is a canonical question about how Unix operating systems report memory usage. Similar Questions: Server refuses to use swap partition Memory Usage in LINUX I have production ...
43
votes
6answers
9k views

Fighting Spam - What can I do as an: Email Administrator, Domain Owner, or User?

This is a Canonical Question about Fighting Spam. Also related: How to stop people from using my domain to send spam? What are SPF records, and how do I configure them? There are ...
58
votes
5answers
8k views

Tips for Securing a LAMP Server

This is a Canonical Question about Securing a LAMP stack What are the absolute guidelines for securing a LAMP server?
67
votes
5answers
39k views

Multiple SSL domains on the same IP address and same port?

This is a Canonical Question about Hosting multiple SSL websites on the same IP. I was under the impression that each SSL Certificate required it's own unique IP Address/Port combination. But the ...
10
votes
2answers
2k views

What are SPF records, and how do I configure them?

This is a canonical question about setting up SPF records. I have an office with many computers that share a single external ip (I'm unsure if the address is static or dynamic). Each computer ...
18
votes
7answers
11k views

How to use DNS/Hostnames or Other ways to resolve to a specific IP:Port

This is a Canonical Question about DNS/Hostnames resolution to IPs/Ports Example 1 I'm running a web server on port 80 and another on port 87. I would like to use DNS so that www.example.com ...
80
votes
2answers
131k views

What is Active Directory Domain Services and how does it work?

This is a Canonical Question about Active Directory Domain Services (AD DS). What is Active Directory? What does it do and how does it work? How is Active Directory organized: Forest, Child ...
17
votes
1answer
2k views

How do you do load testing and capacity planning for databases?

This is a canonical question about capacity planning for databases. Related: Can you help me with my capacity planning? How do you do Load Testing and Capacity Planning for Web ...
142
votes
3answers
91k views

What's the best way of handling permissions for apache2's user www-data in /var/www?

Has anyone got a nice solution for handling files in /var/www? We're running Name Based Virtual Hosts and the apache2 user is www-data. We've got two regular users & root. So when messing with ...
171
votes
9answers
27k views

Heartbleed: What is it and what are options to mitigate it?

This is a Canonical Question about understanding and remediating the Heartbleed security issue. What exactly is CVE-2014-0160 AKA "Heartbleed"? What is the cause, what OSs and versions of OpenSSL ...
46
votes
3answers
16k views

What is a glue record?

This is a Canonical Question about DNS glue records. What exactly (but briefly) is a DNS glue record? Why are they needed and how do they work?
26
votes
5answers
17k views

Windows AD Domain naming recommendations

After experimenting with domains and domain controllers in a virtual environment I realized that having an AD domain named identically to a... well, DNS domain is bad idea (I mean, we have foo.com as ...
9
votes
7answers
5k views

Loopback to forwarded Public IP address from local network - Hairpin NAT

This is a Canonical Question about Hairpin NAT (Loopback NAT). The generic form of this question is: We have a network with clients, a server, and a NAT Router. There is port forwarding on the ...
10
votes
4answers
13k views

Incredible low disk performance on HP DL385 G7

As a test of the Opteron processor family, I bought a HP DL385 G7 6128 with HP Smart Array P410i Controller - no memory. The machine has 20GB ram 2x146GB 15k rpm SAS + 2x250GB SATA2, both in Raid 1 ...
141
votes
2answers
10k views

Why is “chmod -R 777 /” destructive?

This is a Canonical Question about File Permission and Why 777 is "destructive". I'm not asking how to fix this problem, as there are a ton of references of that already on Server Fault ...
62
votes
8answers
6k views

How can a single disk in a hardware SATA RAID-10 array bring the entire array to a screeching halt?

Prelude: I'm a code-monkey that's increasingly taken on SysAdmin duties for my small company. My code is our product, and increasingly we provide the same app as SaaS. About 18 months ago I moved ...
1
vote
1answer
1k views

Outgoing mail from linux not being delivered

I can't seem to send mail through my php scripts or through the linux console on my Centos 5.5 LAMP server, when the email is addressed to go to a domain that is hosted by my box. I think it is ...
34
votes
5answers
12k views

How to understand the memory usage and load average in linux server

I am using a linux server which has 128GB of memory and 24 cores. I use top to see how much it is used. Its output is pasted at the end of the post. Here are two questions: (1) I see that each of the ...
3
votes
1answer
1k views

Prevent mail being marked as spam

This is a canonical question about avoiding outgoing mail being classified as spam. I'm wondering how to prevent my emails from my site being marked as spam? I'm using sendmail. I'm trying to ...
60
votes
15answers
9k views

Hundreds of failed ssh logins

Every night I get hundreds, sometimes thousands, of failed ssh logins on my RedHat 4 server. For firewall reasons from remote sites, I need to run on the standard port. Is there anything I should be ...
50
votes
3answers
45k views

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 ...
59
votes
2answers
76k views

How to Configure Windows Machine to Allow File Sharing with DNS Alias

What process is necessary to configure a Windows environement to allow me to use DNS CNAME to reference servers? I want to do this so that I can name my servers something like SRV001, but still have ...
10
votes
4answers
3k views

How to reset or recover admin account password for MySQL?

I have a MySQL database that I "inherited" and I was not given the admin credentials. I do however have access to the box that it runs on. Is there a way to either recover the admin credentials or ...
33
votes
4answers
2k views

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. ...
68
votes
6answers
56k views

Setting the hostname: FQDN or short name?

I've noticed that the "preferred" method of setting the system hostname is fundamentally different between Red Hat/CentOS and Debian/Ubuntu systems. CentOS documentation and the RHEL deployment guide ...
15
votes
3answers
2k views

Why not use a WAMP stack?

I recently had a talk with some experienced people and they suggested to me not to use a WAMP stack, and instead install apache, mysql and php separately. I don't understand why they have suggested ...
113
votes
4answers
31k views

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 ...
104
votes
15answers
83k views

Why is DNS failover not recommended?

From reading, it seems like DNS failover is not recommended just because DNS wasn't designed for it. But if you have two webservers on different subnets hosting redundant content, what other methods ...
75
votes
6answers
14k views

Why is Enterprise Storage so expensive?

This is a Canonical Question about the Cost of Enterprise Storage. See also the following question: What's the best way to explain storage issues to developers and other users ...
122
votes
8answers
10k views

What’s the point in having “www” in a URL?

Other than for historical reasons, is there is reason to have “www” in a URL. Should I do a permanent redirect from www.xyz.com to xyz.com or xyz.com to www.xyz.com? Which one would you suggest and ...
66
votes
9answers
23k views

How to stop people from using my domain to send spam? [duplicate]

I receive Mailer Daemon messages saying certain emails fail. My domain is itaccess.org which is administered by Google apps. Is there any way I can identify who is sending emails from my domain, and ...
21
votes
3answers
3k views

Find out which process is changing a file

I'm trying to find a reliable way of finding which process on my machine is changing a configuration file (/etc/hosts to be specific). I know I can use lsof /etc/hosts to find out what processes ...
44
votes
6answers
3k views

Reinstall after a Root Compromise?

After reading this question on a server compromise, I started to wonder why people continue to seem to believe that they can recover a compromised system using detection/cleanup tools, or by just ...
226
votes
45answers
47k views

Why is Internet access and Wi-Fi always so terrible at large tech conferences? [closed]

Every tech conference I've ever been to, and I've been to a lot, has had absolutely abysmal Wi-Fi and Internet access. Sometimes it's the DHCP server running out of addresses. Sometimes the backhaul ...
48
votes
2answers
7k views

Why is it so difficult to upgrade between major versions of Red Hat and CentOS?

"Can we upgrade our existing production EL5 servers to EL6?" A simple-sounding request from two customers with completely different environments prompted my usual best-practices answer of "yes, but ...
6
votes
2answers
4k views

Installing a third party application package on CentOS 6.4 fails due to missing dependencies libcrypto.so.10 and libssl.so.10

This is a Canonical Question about OpenSSL binary compatibility issues between Red Hat Enterprise Linux (and its derivatives) 6.4 and 6.5. This issue applies to a wide variety of third party ...
19
votes
3answers
8k views

Linux - real-world hardware RAID controller tuning (scsi and cciss)

Most of the Linux systems I manage feature hardware RAID controllers (mostly HP Smart Array). They're all running RHEL or CentOS. I'm looking for real-world tunables to help optimize performance for ...
16
votes
1answer
7k views

Hosting a ZFS server as a virtual guest

I'm still new to ZFS. I've been using Nexenta but I'm thinking of switching to OpenIndiana or Solaris 11 Express. Right now, I'm at a point of considering virtualizing the ZFS server as a guest within ...
15
votes
3answers
2k views

Can I bind a (large) block of addresses to an interface?

I know that the ip tool lets you bind multiple addresses to an interface (eg, http://www.linuxplanet.com/linuxplanet/tutorials/6553/1/). Right now, though, I'm trying to build something on top of ...

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