48
votes
21answers
15k 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 ...
48
votes
14answers
2k views

Is UPS worthwhile for non-production equipment?

Over the years, I've had to throw away a quite a few bits of computing equipment (and the like): Several ADSL routers with odd symptoms (losing wireless connections, losing wired connections, DHCP ...
48
votes
19answers
6k views

Best Practise and Solutions for Sharing Passwords

We have various passwords that need to be known to more than one person in our company. For example, the admin password to our internet routers, the password for our web-host, and also a few "non-IT" ...
48
votes
10answers
43k views

How to know from which yum repository a package has been installed

After I have installed a package by yum (with multiple repository configured), how can I found from which repository it has been installed? If I run yum info package name (or yum list package name), I ...
48
votes
10answers
12k views

Multiple data centers and HTTP traffic: DNS Round Robin is the ONLY way to assure instant fail-over?

Multiple A records pointing to the same domain seem to be used almost exclusively to implement DNS Round Robin as a cheap load balancing technique. The usual warning against DNS RR is that it is not ...
47
votes
9answers
43k views

Shell command to monitor changes in a file - What's it called again?

I know there was a command on Unix that I could use to monitor a file and see changes that are getting written to it. This was quite useful especially for checking log files. Do you know what it is ...
47
votes
15answers
7k views

Are IP addresses “trivial to forge”?

I was reading through some of the notes on Google's new public DNS service: Performance Benefits Security Benefits I noticed under the security section this paragraph: Until a standard ...
47
votes
8answers
104k views

How to automate SSH login with password?

How to automate SSH login with password? I'm configuring my test VM, so heavy security is not considered. SSH chosen for acceptable security with minimal configuration. ex) echo password | ssh ...
47
votes
2answers
3k views

Mysterious visitor to hidden PHP page

On my website, I have a "hidden" page that displays a list of the most recent visitors. There exist no links at all to this single PHP page, and, theoretically, only I know of its existence. I check ...
47
votes
3answers
38k 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 ...
47
votes
2answers
5k 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 ...
47
votes
1answer
2k 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 ...
47
votes
6answers
4k views

What should NOT be managed by puppet?

I'm learning my way through configuration management in general and using puppet to implement it in particular, and I'm wondering what aspects of a system, if any, should not be managed with puppet? ...
46
votes
14answers
26k views

Top level domain for private networks?

On our office network we have an internal DNS and all the hostnames are whatever.lan. On my VMware VMs, on their host-only network I call them whatever.vm. We now have a private IP space network in ...
46
votes
17answers
8k views

Do you skip a rack unit between servers?

It seems like there's a lot of disagreement in mindsets when it comes to installing rackmount servers. There have been threads discussing cable arms and other rackmount accessories, but I'm curious: ...
46
votes
12answers
4k views

Good reasons to keep 32-bit Microsoft Windows desktop OSes

Server software has been 64-bit only for a while now (Since Server 2008 R2 for Windows, even earlier for Exchange and Sharepoint) and even Ubuntu are pushing you away from 32-bit versions for their ...
46
votes
4answers
13k views

Where does email sent to *@example.com go? [closed]

So I've wondered this for a long time. Where does email sent to *@example.com go? If I accidentally sent sensitive information to *@example.com would some evil person (potentially at the IANA) be ...
46
votes
8answers
2k views

What are the advantages of tape drives?

IBM still develop and sell tape drives today. The capacity of them seems to be on a par with today's hard drives, but the search time and transfer rate are both significantly lower than that of hard ...
46
votes
9answers
54k views

When does `cron.daily` run?

When do entries in cron.daily (and .weekly and .hourly) run, and is it configurable? I haven't found a definitive answer to this, and am hoping there is one. I'm running RHEL5 and CentOS 4, but for ...
46
votes
11answers
87k views

How do I find if there is a rogue DHCP server on my Network?

What's the best approach towards determining if I have a rogue DHCP server inside my network? I'm wondering how most admins approach these kinds of problems. I found "DHCP Probe" ...
46
votes
9answers
56k views

What's the best way to move c:\users to d:\users under vista/W7 [closed]

I just installed Windows 7 RC1 and want to move c:\users to d:\users. What's the best way to do this? Due to the fact that Windows 7 creates a reserved partition that is mounted as C: in the ...
46
votes
8answers
86k views

What limits the maximum number of connections on a Linux server?

What kernel parameter or other settings control the maximum number of TCP sockets that can be open on a Linux server? What are the tradeoffs of allowing more connections? I noticed while load testing ...
46
votes
6answers
29k views

Can anyone explain precisely what IOWait is?

As much as I have read about iowait, it is still mystery to me. I know it's the time spent by the CPU waiting for a IO operations to complete, but what kind of IO operations precisely? What I am also ...
45
votes
9answers
10k views

What's the difference between apt-get and aptitude?

I don't get why there are two different programs in a minimal install to install software. Don't they do the same thing? Is there a big difference? I have read everywhere to use aptitude over apt-get ...
45
votes
12answers
3k views

What should I pay attention to when I'm buying a network switch?

Since I'm not a hardware expert, I don't know what features make a network switch a good network switch. What should I pay attention, when I'm comparing the different models from different vendors?
45
votes
5answers
371k views

How to determine the hostname from an IP address in a Windows network?

My LAN has 50 Windows hosts. At the Windows command line I try ping to get the IP address of a running Windows machine. The question is how to get hostname of a specific IP address in the same ...
45
votes
12answers
94k views

Using wget to recursively download whole FTP directories

I want to copy all of the files and folders from one host to another. The files on the old host sit at /var/www/html and I only have FTP access to that server, and I can't TAR all the files. Regular ...
45
votes
2answers
24k 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 ...
45
votes
10answers
101k views

Run Oracle SQL script and exit from sqlplus.exe via command prompt

I would like to run an Oracle script through SQL Plus via a Windows command prompt. The script does not contain an "exit" command, but I would still like SQL Plus to exit, returning control to the ...
45
votes
15answers
40k views

Is FreeNAS reliable?

FreeNAS seems like a great product with a full checklist of features, even iSCSI. But how reliable is it? There are a few scary stories about lost data, for example here. Here is another example. If ...
45
votes
6answers
146k views

How can I figure out my LDAP connection string?

We're on a corporate network thats running active directory and we'd like to test out some LDAP stuff (active directory membership provider, actually) and so far, none of us can figure out what our ...
45
votes
3answers
6k 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
5answers
45k views

Which to install: Apache Worker or Prefork? What are the (dis-)advantages of each?

Based on the descriptions for both the Prefork and Worker MPM, it seems the prefork type is somewhat outdated, but I can't really find a proper comparison of the two types. What i'd like to know: ...
45
votes
2answers
5k 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 ...
44
votes
5answers
7k 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 ...
44
votes
7answers
3k views

How to take full ownership of an IP address?

My business is... troublesome. What I do is legal in every country on earth, but some people don't like it, and make it so tough on my poor ISPs that I am forced to go looking for new providers more ...
44
votes
7answers
51k views

How to determine JAVA_HOME on Debian/Ubuntu?

On Ubuntu it is possible to have multiple JVMs at the same time. The default one is selected with update-alternatives. But this does not set the JAVA_HOME environment variable, due to a debian policy. ...
44
votes
6answers
77k views

How do I create user accounts from the Terminal in Mac OS X 10.5?

I would like to be able to create new users in Mac OS X 10.5 remotely after ssh'ing into the machine. How do I do this?
44
votes
8answers
2k views

How is fire spread in server rooms and datacenters?

Every now and then I read that a severe fire has happened in some datacenter, lots of equipment has been damaged and customers have gone offline. Now I wonder what is there to support and spread fire? ...
44
votes
4answers
18k views

How do I edit git's history to correct an incorrect email address/name

When I started using git I just did a git init and started calling add and commit. Now I am starting to pay attention and I can see that my commits are showing up as cowens@localmachine, rather than ...
44
votes
3answers
4k views

What is the difference between a soft (symbolic) link and a hard link?

I hear that you can now create soft links in Vista too. So, what is the difference between a soft (symbolic) link and a hard link on UNIX/Linux/Vista? Are there advantages of using one over the ...
44
votes
3answers
54k views

Is there a way to view the members of an Active Directory group if you aren't a domain admin and can't log into to a domain controller?

Is there a way to view the members of an Active Directory group if you aren't a domain admin and can't log into to a domain controller?
44
votes
14answers
85k views

What is the correct temperature for a server room?

When I was working in our server room, I noticed that it was very cold. I know that the server room has to be cold to offset the heat of the servers, but perhaps it is TOO cold. What is an ...
43
votes
6answers
3k views

Why do we still have such small email attachment filesize restrictions? [closed]

What's the technical limitation preventing us, in the glorious year 2011, from emailing each other 1GB files? Or is it just the main email platforms dragging their feet? If I can set my inbox to ...
43
votes
40answers
4k views

How do you manage your passwords?

Obviously seeing as how many of us here are system administrator type people, we have a lot of passwords strung out across numerous systems and accounts. Some of them are low priority, others could ...
43
votes
8answers
254k views

Command line to list users in a Windows Active Directory group?

Is there a command line way to list all the users in a particular Active Directory group? I can see who is in the group by going to Manage Computer --> Local User / Groups --> Groups and double ...
43
votes
8answers
3k views

Why would I need a firewall if my server is well configured?

I admin a handful of cloud-based (VPS) servers for the company I work for. The servers are minimal ubuntu installs that run bits of LAMP stacks / inbound data collection (rsync). The data is large ...
43
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 ...
43
votes
3answers
45k views

How to delete Instances in Amazon EC2 ? Change Pair Key?

How to remove Instances ? I test some Instances and now I terminate it. So, I want to remove it. I can't find delete or remove action. I just found terminate. How to change the pair key ? I don't ...
43
votes
9answers
84k views

Creating a virtual machine in VirtualBox from a physical one

Is there any way to create a virtual machine that you can use in VirtualBox from a physical installation that you have? For instance, if I have Windows XP installed on a physical computer and want to ...

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