All Questions
18,422
questions
632
votes
13
answers
164k
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 ...
- 6,420
45
votes
5
answers
27k
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 ...
- 12.1k
144
votes
4
answers
43k
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 ...
- 80.1k
285
votes
5
answers
115k
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 ...
- 84k
389
votes
7
answers
942k
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 ...
- 4,301
476
votes
8
answers
185k
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 ...
97
votes
8
answers
194k
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 ...
- 1,825
125
votes
5
answers
76k
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 ...
- 12k
191
votes
5
answers
26k
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 ...
- 25.3k
155
votes
2
answers
972k
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 ?
- 116k
187
votes
73
answers
247k
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 ...
190
votes
2
answers
47k
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?
- 101k
59
votes
2
answers
24k
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 ...
- 749
111
votes
6
answers
66k
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 ...
- 78.1k
372
votes
6
answers
568k
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/...
- 13.5k
64
votes
12
answers
97k
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 ...
- 1,531
98
votes
5
answers
119k
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 ...
- 1,582
165
votes
3
answers
108k
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 ...
- 32.8k
57
votes
10
answers
77k
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 ...
- 1,125
45
votes
3
answers
10k
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 ...
user135199
205
votes
5
answers
149k
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?
- 3,107
110
votes
5
answers
79k
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 ...
- 7,403
30
votes
4
answers
11k
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 ...
- 405
31
votes
5
answers
14k
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 ...
- 446
175
votes
18
answers
280k
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 ...
- 2,325
151
votes
2
answers
327k
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, ...
- 101k
10
votes
1
answer
6k
views
How can I forward requests from my web server?
This is a Canonical Question about reverse proxies, how they work and how they are configured.
How can I serve requests from a service on a different port or from a different server with the same ...
- 24.2k
103
votes
6
answers
24k
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?
- 1,031
13
votes
6
answers
45k
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 ...
- 198k
271
votes
2
answers
86k
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)...
- 2,413
217
votes
8
answers
347k
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 ...
- 25.4k
100
votes
21
answers
53k
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. ...
- 1,965
36
votes
2
answers
11k
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 ...
- 12k
67
votes
9
answers
87k
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, ...
- 905
6
votes
1
answer
3k
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 ...
- 171
33
votes
2
answers
4k
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 ...
- 32.8k
554
votes
11
answers
592k
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 ...
- 8,482
60
votes
5
answers
43k
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 ...
- 1,497
26
votes
7
answers
66k
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. ...
- 361
109
votes
8
answers
23k
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 ...
- 3,359
30
votes
5
answers
14k
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,...
- 403
234
votes
4
answers
182k
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 ...
- 8,573
77
votes
3
answers
200k
views
How to handle relative urls correctly with a reverse proxy
I have a reverse proxy setup as follows in Apache:
Server A with address www.example.com/folder is the reverse proxy server.
It maps to: Server B with address test.madeupurl.com
This kind of works....
- 879
51
votes
7
answers
34k
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 ...
- 1,714
41
votes
7
answers
57k
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%...
- 781
309
votes
5
answers
698k
views
Nginx reverse proxy + URL rewrite
Nginx is running on port 80, and I'm using it to reverse proxy URLs with path /foo to port 3200 this way:
location /foo {
proxy_pass http://localhost:3200;
...
- 3,255
163
votes
5
answers
33k
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 ...
- 14.5k
12
votes
4
answers
37k
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 ...
- 4,330
202
votes
4
answers
280k
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:...
- 2,123
32
votes
4
answers
52k
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 ...
- 198k