142
votes
4answers
46k 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 ...
162
votes
7answers
20k 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 ...
90
votes
6answers
23k 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 ...
60
votes
2answers
15k 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 ...
14
votes
6answers
8k 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 ...
252
votes
45answers
62k 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 ...
134
votes
15answers
114k 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 ...
64
votes
22answers
25k 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 ...
53
votes
8answers
42k views

What is “anycast” and how is it helpful?

I'd never heard of anycast until a few seconds ago when I read this SF post. The wikipedia entry on it is quite formal and doesn't really evoke a mental picture of how it would be used. Can someone ...
23
votes
4answers
37k views

How do I tell if my Windows server is swapping?

I'm using Process Explorer to monitor my windows server while it reconstructs some data. It's primarily a CPU intensive process, but I want to make sure it's not swapping. How can I tell if it is ...
48
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 ...
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 ...
38
votes
2answers
138k 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 ...
26
votes
3answers
12k 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 ...
18
votes
4answers
17k 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 ...
6
votes
3answers
11k 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 ...
7
votes
13answers
30k 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 ...
72
votes
2answers
69k 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 ...
66
votes
5answers
186k views

How can I port forward with iptables?

I want connections coming in on ppp0 on port 8001 to route 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 ...
78
votes
13answers
32k 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 ...
21
votes
4answers
8k views

Best Practices for preventing you from looking like a spammer [duplicate]

I'd like to feel more confident setting up mail for my clients with regards to false positives. Here's what I know: SPF records are good, but not every spam filter service/software (SFSS) uses ...
10
votes
1answer
18k views

How exactly does a SAS SFF-8087 breakout cable work? + RAID/connection questions

Please let me know if my question does not makes any sense as I am not sure if I am interpreting it correctly from my thoughts due to my lack of technical knowledge on this. If I am using a ...
10
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 ...
50
votes
3answers
94k views

How can I connect to a Windows server using a Command Line Interface? (CLI)

Especially with the option to install Server Core in Server 2008 and above, connecting to Windows servers over a CLI is increasingly useful ability, if not one that's very widespread amongst Windows ...
30
votes
23answers
50k 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)
16
votes
6answers
20k 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 ...
35
votes
1answer
19k 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 ...
6
votes
4answers
2k views

Multiple servers acting like a single one with all the hardware?

by now I have 10 servers for hpc, power computing oriented. My users need to launch several processes using qmake. The users are used to work with ubuntu 9.10, and the software from the repositories ...
39
votes
9answers
52k 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 ...
19
votes
6answers
8k views

Avoid linux out-of-memory application teardown

I'm finding that on occasion my Linux box runs out of memory and it starts tearing down random processes to deal with it. I'm curious what administrators do to avoid this? Is the only real ...
4
votes
1answer
2k views

Set up BIND9 as DNS Firewall

With OpenDNS now needing one to be on the pro package to have filtering turned on, being on a tight budget, we are in need of free DNS filtering. After reading this link on how to block domains with ...
4
votes
3answers
4k 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 ...
145
votes
26answers
280k views

Using DD for disk cloning

There's been a number of questions regarding disk cloning tools and dd has been suggested at least once. I've already considered using dd myself, mainly because ease of use, and that it's readily ...
73
votes
5answers
49k 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 ...
15
votes
3answers
20k views

How to configure postfix to pipe all incoming email to a script?

Using postfix, I'd like all incoming mail, to any address (including those that don't map to local users) to be piped to a script. I've tried configuring mailbox_command in /etc/postfix/main.cf: ...
27
votes
10answers
27k views

How do I know if my Linux server has been hacked?

What are the tell-tale signs that a Linux server has been hacked? Are there any tools that can generate and email an audit report on a scheduled basis?
33
votes
5answers
6k 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, ...
23
votes
8answers
5k views

accidently ran “chown www-data:www-data / -R” as root

i just ran this a few seconds ago, i managed to do ctrl-c as soon as i realized what i started doing. so far in the only dir its started going through is /bin im afraid to do anything else, so far ...
61
votes
11answers
18k views

Why drop caches in Linux?

In our servers we have a habit of dropping caches at midnight. sync; echo 3 > /proc/sys/vm/drop_caches When I run the code it seems to free up lots of RAM, but do I really need to do that. ...
23
votes
3answers
38k 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 ...
13
votes
4answers
11k 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 ...
12
votes
2answers
4k 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 ...
0
votes
2answers
2k views

Can't resolve issue: iptables: No chain/target/match by that name

So I am trying to setup shorewall firewall on my linux vps. The vps is running ubuntu 12.10. When I type $ shorewall check I get this error. iptables: No chain/target/match by that name. ERROR: ...
199
votes
11answers
64k 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 ...
142
votes
2answers
60k views

How do I select which Apache MPM to use?

I'm a little confused between the different MPMs offered by Apache - 'worker', 'event', 'prefork', etc. What are the major differences between them, and how can I decide which one will be best for a ...
65
votes
17answers
30k 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 ...
56
votes
2answers
80k views

SFTP logging: is there a way?

I'm wondering if there is a way to log commands received by the server. It can be all SSH commands, as long as it includes information on commands related to file transfer. I'm having issues with an ...
51
votes
1answer
45k views

How long does it take for DNS records to propagate?

This is a Canonical Question about DNS Propagation How long does it take for an the various types of records to propagate? Do some propagate faster than others? Why does it take time for DNS ...
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 ...
31
votes
5answers
12k views

Debugger for Iptables

I'm looking for an easy way to follow a packet through the iptables rules. This is not so much about logging, because I don't want to log all traffic (and I only want to have LOG targets for very few ...

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