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608
votes
13answers
142k 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 ...
45
votes
5answers
24k 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 want to ...
133
votes
3answers
34k 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 databases? I have a ...
268
votes
5answers
101k views

Redirect, Change URLs or Redirect HTTP to HTTPS in Apache - Everything You Ever Wanted 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 includes ...
258
votes
6answers
491k views

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

This is a Canonical Question about using cron & crontab. You have been directed here because the community is fairly sure that the answer to your question can be found below. If your question is ...
450
votes
8answers
163k 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 by ...
88
votes
8answers
159k 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 ...
115
votes
5answers
66k 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 databases? What are some ...
180
votes
5answers
22k 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 ...
187
votes
73answers
242k views

What tool do you use to monitor your servers?

For a more comprehensive list of monitoring tools and their features, check out this Wikipedia page. As the question states, what are the most commonly used tools used for this task and what are ...
123
votes
2answers
732k views

What causes the 'Connection Refused' message?

This is a Canonical Question about Connection Refused We see a lot of questions to the effect When I try to connect to a system I get a message Connection refused Why is this ?
183
votes
2answers
42k 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?
53
votes
2answers
20k 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 ...
109
votes
6answers
61k 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 so ...
329
votes
6answers
430k 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/. /var/...
92
votes
5answers
103k views

Windows Active Directory naming best practices?

This is a Canonical Question about Active Directory domain naming. After experimenting with Windows domains and domain controllers in a virtual environment, I've realized that having an active ...
50
votes
12answers
63k 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 ...
110
votes
5answers
73k 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 ...
164
votes
4answers
109k 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?
44
votes
3answers
8k 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 ...
52
votes
9answers
57k 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 goes to ...
131
votes
3answers
68k views

Why can't a CNAME record be used at the apex (aka root) of a domain?

This is a Canonical Question about CNAMEs at the apices (or roots) of zones It's relatively common knowledge that CNAME records at the apex of a domain are a taboo practice. Example: example.com. IN ...
30
votes
4answers
9k views

Prevent mail being marked as spam

This is a canonical question about avoiding outgoing mail being classified as spam. Also related: Fighting Spam - What can I do as an: Email Administrator, Domain Owner, or User? What ...
29
votes
5answers
12k views

Why not use a WAMP stack?

This is a canonical question about the use of a *AMPP's 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 ...
150
votes
2answers
316k 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 Domain, ...
128
votes
18answers
194k views

Disk full, du tells different. How to further investigate?

I have a SCSI disk in a server (hardware Raid 1), 32G, ext3 filesytem. df tells me that the disk is 100% full. If I delete 1G this is correctly shown. However, if I run a du -h -x / then du tells me ...
98
votes
6answers
21k 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?
13
votes
6answers
39k views

ZFS SAS/SATA controller recommendations

I've been working with OpenSolaris and ZFS for 6 months, primarily on a Sun Fire x4540 and standard Dell and HP hardware. One downside to standard Perc and HP Smart Array controllers is that they do ...
258
votes
2answers
74k 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 (reinstall OS)...
95
votes
21answers
45k views

Should we host our own nameservers?

This is a Canonical Question about whether to outsource DNS resolution for ones own domains I currently have my ISP providing DNS for my domain, but they impose limitations on adding records. ...
67
votes
9answers
79k views

What a beginner should know/learn for sysadmin job?

This is a Canonical Question about System Administration Careers When I start my job as System Administrator, what basics skills should I know/learn? Are there any key differences for Network, ...
31
votes
2answers
3k views

Why is geo-redundant DNS necessary for small sites?

This is a Canonical Question about DNS geo-redundancy. It's extremely common knowledge that geo-redundant DNS servers located at separate physical locations are highly desirable when providing ...
6
votes
1answer
2k views

Excessive number of sleeping processes in CentOS - howto diagnose? [closed]

I have a a large number of sleeping processes, about 600, the majority of which are Apache processes. Should I kill all these sleeping processes, or will that make Apache fail completely? Why are ...
191
votes
7answers
271k 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 ...
35
votes
2answers
9k 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 sites? I'm looking to ...
26
votes
6answers
53k views

Third-party SSD solutions in ProLiant Gen8 servers

I was wondering if anyone had any specific experience using Intel DC3700 SSDs (or similar) in the HP (DL380p) Gen8 servers? I'm upgrading a set of database servers that use direct-attached storage. ...
58
votes
5answers
39k 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 ...
105
votes
8answers
20k 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 our ...
221
votes
4answers
166k views

What's the best way of handling permissions for Apache 2'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 Apache 2 user is www-data. We've got two regular users & root. So when messing with ...
38
votes
7answers
23k views

Is there a name based virtual host SSH reverse proxy?

I've grown quite fond of HTTP reverse proxies in our development environment and found the DNS based virtual host reverse proxy quite useful. Having only one port (and the standard one) open on the ...
162
votes
5answers
31k views

Are SSD drives as reliable as mechanical drives (2013)?

SSD drives have been around for several years now. But the issue of reliability still comes up. I guess this is a follow up from this question posted 4 years ago, and last updated in 2011. It's now ...
26
votes
5answers
10k 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 IPv6,...
12
votes
4answers
35k views

Incredibly low disk performance on HP ProLiant 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 ...
29
votes
4answers
44k views

What happens when the USB key or SD card I've installed VMware ESXi on fails?

An SD (SDHC) card installed in an HP ProLiant DL380p Gen8 server running VMware ESXi just failed :( I encountered some ominous looking messages on the vCenter console and in the HP ProLiant ILO event ...
525
votes
11answers
499k views

In Nginx, how can I rewrite all http requests to https while maintaining sub-domain?

I want to rewrite all http requests on my web server to be https requests, I started with the following: server { listen 80; location / { rewrite ^(.*) https://mysite.com$1 ...
176
votes
2answers
209k 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 Swap:...
203
votes
9answers
32k 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 are ...
34
votes
7answers
43k views

du vs. df difference [duplicate]

I have a fileserver where df reports 94% of / full. But according to du, much less is used: # df -h / Filesystem Size Used Avail Use% Mounted on /dev/sda3 270G 240G 17G 94%...
82
votes
15answers
16k 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 ...
69
votes
3answers
212k views

How does ServerName and ServerAlias work?

It's the following part of a virtual host config that I need further clarification on: <VirtualHost *:80> # Admin email, Server Name (domain name), and any aliases ServerAdmin example@...

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