25
votes
1answer
1k 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 ...
139
votes
16answers
120k 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 ...
32
votes
5answers
10k views

Are VMware ESXi 5 patches cumulative?

This seems basic, but I'm confused about the patching strategy involved with manually updating standalone VMware ESXi hosts. The VMware vSphere blog attempts to explain this, but the actual process is ...
18
votes
4answers
20k 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 ...
7
votes
2answers
608 views

What is the role of NS records at the apex of a DNS domain?

$ORIGIN example.com. ; not necessary, using this to self-document $TTL 3600 @ IN SOA ns1.example.com. admin.example.com. ( 1970010100 7200 1800 1209600 300) @ ...
3
votes
1answer
896 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 ...
346
votes
7answers
280k 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 ...
76
votes
16answers
58k views

Alternatives to Splunk?

I'm pretty impressed with Splunk, especially version 4. Pretty graphs, alerting (Enterprise only), and fast, accurate, searching. It's a great product. However, the cost just way too high to consider ...
171
votes
7answers
23k 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 ...
55
votes
8answers
50k views

What is “anycast” and how is it helpful?

I'd never heard of anycast until a few seconds ago when I read "What are some cool or useful server/networking tricks?". The wikipedia "Anycast" article on it is quite formal and doesn't really evoke ...
7
votes
13answers
32k views

HP Proliant DL380 G4 - Can this server still perform in 2011?

Can the HP Proliant DL380 G4 series server still perform at high a quality in the 2011 IT world? This may sound like a weird question but we are a very small company whose primary business is NOT IT ...
11
votes
1answer
6k views

In DNS can an IN NS point to a CNAME?

Is it allowed to have an NS record be a CNAME? E.g.: subdomain.example.com. IN NS ns1.example.com. ns1.example.com. CNAME foo.example.com. foo.example.com. IN A 10.1....
17
votes
6answers
21k views

Cygwin SSHd Autoblock Failed Logins

I'm running Cygwin with an SSH deamon on a Windows Server 2008 machine. I was looking at the Event Viewer and noticed as much as 5 to 6 failed login attempts per second (brute force) for the last week ...
20
votes
5answers
4k 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,...
44
votes
9answers
65k 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 ...
49
votes
6answers
4k 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 ...
36
votes
1answer
22k views

HP ProLiant DL360 G7 hangs at “Power and Thermal Calibration” screen

I have a new HP ProLiant DL360 G7 system that is exhibiting a difficult-to-reproduce issue. The server randomly hangs at the "Power and Thermal Calibration in Progress..." screen during the POST ...
2
votes
1answer
2k 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 ...
96
votes
6answers
25k 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 ...
72
votes
23answers
27k views

rm on a directory with millions of files

Background: physical server, about two years old, 7200-RPM SATA drives connected to a 3Ware RAID card, ext3 FS mounted noatime and data=ordered, not under crazy load, kernel 2.6.18-92.1.22.el5, uptime ...
73
votes
5answers
204k views

How can I port forward with iptables?

I want connections coming in on ppp0 on port 8001 to be routed to 192.168.1.200 on eth0 on port 8080. I've got these two rules -A PREROUTING -p tcp -m tcp --dport 8001 -j DNAT --to-destination 192....
36
votes
4answers
3k 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. ...
85
votes
13answers
34k views

Why is RAID not a backup?

When someone mentions RAID in a conversation about backups, invariably someone declares that "RAID is not a backup." Sure, for striping, that's true. But what's the difference between redundancy and ...
62
votes
2answers
17k 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 ...
9
votes
5answers
24k views

Why does Red Hat Linux report less free memory on the system than is actually available?

I have a relatively small home Red Hat Linux server (about 8 GB RAM). I don't use it for much other than running some home grown apps to keep track of various things. The only real things running on ...
5
votes
3answers
5k views

Permission denied in vhost document root

I'm having a problem setting up a vhost on Apache 2.4, using CentOS 6.3. This question seems to have been answered several times on this forum, but none of the solutions work for me. Basically, I ...
78
votes
2answers
80k views

How do VLANs work?

What are VLANs? What problems do they solve? I'm helping a friend learn basic networking, as he's just become the sole sysadmin at a small company. I've been pointing him at various questions/answers ...
46
votes
2answers
154k views

Can I have multiple DHCP servers on one network?

This is a Canonical Question about Redundant DHCP Servers. Is it possible to have more than one DHCP server on the same LAN? What are the implications of doing this? What happens if there is more ...
86
votes
9answers
71k 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 ...
33
votes
23answers
54k views

Finding the Public IP address in a shell script

I can find my IP address using ifconfig or hostname -i command. But how do I find my Public IP? (I have a static public IP but I want to find it out using unix command)
24
votes
3answers
45k views

What should the order of DNS servers be for an AD Domain Controller and Why?

This is a Canonical Question about Active Directory DNS Settings. Related: What is Active Directory and how does it work? Assuming an environment with multiple domain controllers (...
6
votes
3answers
12k views

FTP and Apache permission issues

Im having issues as to which user should own my www directory - ftp or apache? When set to the ftp user, the user can add, remoe and easily modify files but php file system actions generate permission ...
14
votes
2answers
8k 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 ...
13
votes
4answers
12k views

Set root domain record to be a CNAME

I need to create an NS record for a domain that is a CNAME, for the purpose of having two domains pointed at one IP, and not having to maintain the current IP address in two different places. The DNS ...
196
votes
22answers
56k views

Is it normal to get hundreds of break-in attempts per day?

I just checked my server's /var/log/auth.log and found that I'm getting over 500 failed password/break-in attempt notifications per day! My site is small, and its URL is obscure. Is this normal? ...
210
votes
11answers
66k views

Can I nohup/screen an already-started process?

I'm doing some test-runs of long-running data migration scripts, over SSH. Let's say I start running a script around 4 PM; now, 6 PM rolls around, and I'm cursing myself for not doing this all in ...
85
votes
12answers
15k views

What solutions exist to allow the use of revision control for server configuration files? [closed]

In an environment with multiple system administrators, I see a few advantages to adding the server config files into a revision control system. Most notable are the ability to track changes, who made ...
73
votes
17answers
32k views

Switching to IPv6 implies dropping NAT. Is that a good thing?

This is a Canonical Question about IPv6 and NAT Related: How does IPv6 subnetting work and how does it differ from IPv4 subnetting? How can I 'dip my toes' into dynamic IPv6 ...
75
votes
6answers
54k views

Top level domain/domain suffix for private network?

At our office, we have a local area network with a purely internal DNS setup, on which clients all named as whatever.lan. I also have a VMware environment, and on the virtual-machine-only network, I ...
37
votes
7answers
30k views

Log all commands run by admins on production servers

It is company policy for admins to login to the servers via a personal username, and then run sudo -i to become root. Upon running sudo -i, sudo will create an environmental variable called SUDO_USER,...
49
votes
3answers
3k views

Assessing equipment damage following a lightning strike - Should I have planned more?

One of my client's sites received a direct lightning hit last week (coincidentally on Friday the 13th!). I was remote to the site, but working with someone onsite, I discovered a strange pattern of ...
33
votes
5answers
7k views

What to look for in a server rack?

I'm looking to purchase a rack/enclosure for some servers. As this is my first time shopping for this type of equipment, I need to know what to look for. I'm asking not only about how to buy the rack, ...
21
votes
3answers
85k views

How to run VMWare ESX or ESXi in a virtual machine?

Can VMWare ESX or ESXi be installed and used inside a virtual machine? It can be installed inside VMWare Workstation or Server, but then it doesn't work; the main symptoms are: It runs REALLY ...
16
votes
4answers
1k views

SSL certificate selection based on host-header: is it possible?

Is it possible for a web server to select an SSL certificate to use based on the host-header of the incoming connection, or is that information that is only available after the SSL connection is ...
3
votes
1answer
3k views

Openfiler iSCSI performance

Hoping someone can point me in the right direction with some iSCSI performance issues I'm having. I'm running Openfiler 2.99 on an older ProLiant DL360 G5. Dual Xeon processor, 6GB ECC RAM, Intel ...
13
votes
2answers
5k views

Website and Active Directory domain share the same name

In our network the name of the network domain is also the domain of the organization's website (say, example.com). Externally, people can enter example.com to visit our website, but internally, this ...
2
votes
1answer
84 views

Hosting multiple distinct folders for distinct domains

I have a VPS that I've installed a Apache Web Server on. What I want to do is forward my own website domains to that server and host those websites' files inside my Apache Web Server. As far as I ...
282
votes
160answers
214k views

Useful Command-line Commands on Windows

The aim for this Wiki is to promote using a command to open up commonly used applications without having to go through many mouse clicks - thus saving time on monitoring and troubleshooting Windows ...
367
votes
5answers
140k views

Anyone else experiencing high rates of Linux server crashes during a leap second day?

*NOTE: if your server still has issues due to confused kernels, and you can't reboot - the simplest solution proposed with gnu date installed on your system is: date -s now. This will reset the ...
254
votes
45answers
64k views

What are the obstacles to providing reliable Internet access and Wi-Fi 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 ...

15 30 50 per page