61
votes
3answers
25k 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?
61
votes
3answers
86k 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?
60
votes
3answers
75k views

How to add dependency on a Windows Service AFTER the service is installed

I have a Windows Service that makes use of a SQL Server database. I don't have control over the installation of the service, but would like to add a dependency on the service to ensure that it starts ...
60
votes
2answers
50k 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 ...
60
votes
5answers
17k views

Active Directory explained

If you had to explain Active Directory to someone how would you explain it?
60
votes
20answers
24k views

Should we host our own nameservers?

I currently have my ISP providing DNS for my domain, but they impose limitations on adding records. Therefore, I am thinking about running my own DNS. Do you prefer to host your own DNS, or is it ...
60
votes
9answers
47k views

Is it possible to detach a process from its terminal? (Or, “I should have used screen!”) [duplicate]

Possible Duplicate: Can I nohup/screen an already-started process? On Unix (specifically, Linux), I've started a job in a regular ssh->bash session. I'd like to leave work soon, but I now ...
59
votes
17answers
26k 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 ...
59
votes
7answers
5k views

DNS failing to propagate worldwide

I haven't changed anything related to the DNS entry for serverfault.com, but some users were reporting today that the serverfault.com DNS fails to resolve for them. I ran a justping query and I can ...
59
votes
5answers
137k views

How to make Windows 7 USB flash install media from Linux?

I have: ISO image of Windows 7 install media 4 GB USB flash drive no DVD drive Linux installed
59
votes
4answers
25k 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 ...
59
votes
3answers
39k views

What is archive mode in rsync?

I know you can use -a or --archive to activate archive mode when using rsync. Unfortunately, I have no idea what archive mode is supposed to do, and the man page is not at all explicit about what this ...
59
votes
2answers
27k views

ssh hostname returns “Bad owner or permissions on ~/.ssh/config”

When I try to ssh to another box, I get this strange error $ ssh hostname Bad owner or permissions on ~/.ssh/config But I made sure that I own and have rw permissions on the file: ls -la ~/.ssh/ ...
59
votes
22answers
21k 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 ...
59
votes
11answers
16k 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 ...
58
votes
11answers
228k views

How can I choose between using my ISP's DNS, or Google's 8.8.8.8? [closed]

It seems like a good idea to use Google's public DNS 8.8.8.8 and 8.8.4.4 because it's really fast -- much faster than my own ISP's DNS! -- and probably more reliable, too. That seems like a ...
58
votes
22answers
10k views

How the heck is http://to./ a valid domain name?

Apparently it's a URL shortener. It resolves just fine in Chrome and Firefox. How is this a valid top-level domain? Update: for the people saying it's browser shenanigans, why is it that: ...
58
votes
11answers
127k 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 through searching, ...
58
votes
1answer
31k views

How do I change my private key passphrase?

I have an existing public/private key pair, the private key is password protected, the encryption may be either RSA or DSA. These keys are the kind you generate with ssh-keygen and generally store ...
58
votes
1answer
58k views

How do I add Access-Control-Allow-Origin in NGINX?

How do I set the Access-Control-Allow-Origin header so I can use web-fonts from my subdomain on my main domain? Notes: You'll find examples of this and other headers for most HTTP servers in the ...
58
votes
12answers
90k views

Subversion error: (405 Method Not Allowed) in response to MKCOL

I am getting the following error while trying to commit a new directory addition. svn: Commit failed (details follow): svn: Server sent unexpected return value (405 Method Not Allowed) in response to ...
58
votes
11answers
22k views

How does a team of Systems Administrators share passwords securely?

What are best practices for sharing hundreds of passwords among a few people? These passwords protect mission critical data, and cannot ever be visible beyond a small team.
57
votes
11answers
14k 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. ...
57
votes
6answers
474k 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 ...
57
votes
10answers
47k views

memcache vs memcached?

I want to use memcached http://www.danga.com/memcached/ I have installed it through yum install memcached But now I need to connect to PHP, and there is an extension named memcache and one named ...
57
votes
7answers
87k views

how to check if a library is installed?

In linux, how do I check if a library is installed or not? (from the command line of course). In my specific case now, I want to check whether libjpeg is installed.
57
votes
7answers
6k views

What are the drawbacks of running a database inside a virtual machine? How do I overcome them? [closed]

Running anything inside a virtual machine will have some level of performance hit, but how much does it really impact the performance of a database system? I found this academic reference paper with ...
56
votes
9answers
68k views

How can I export the privileges from MySQL and then import to a new server?

I know how to export/import the databases using mysqldump & that's fine but how do I get the privileges into the new server. For extra points, there are a couple of existing databases on the new ...
56
votes
10answers
4k views

How to extinguish a small fire in a server rack to minimize damage to surrounding equipment?

Suppose I have a rack with several servers and other stuff. One of servers overheats severely and either starts smoking or catches fire while there's a serviceman nearby. If anything similar happens ...
56
votes
6answers
17k views

Why use Chef/Puppet over shell scripts?

New to Puppet and Chef tools. Seems like the job that they are doing can be done with shell scripting. Maybe it was done in shell scripts until these came along. I would agree they are more readable. ...
56
votes
5answers
66k views

Clean way to write complex multi-line string to a variable

I need to write some complex xml to a variable inside a bash script. The xml needs to be readable inside the bash script as this is where the xml fragment will live, it's not being read from another ...
56
votes
5answers
61k views

How to setup passwordless `sudo` on Linux?

How can passwordless sudo access be setup on either RHEL (Fedora, CentOS, etc) or Ubuntu distributions? (If it's the same across distros, that's even better!) Setting: personal and/or lab/training ...
56
votes
3answers
5k views

Is a VM with 2 CPUs really faster than one with 4 CPUs?

Our IT created a VM with 2 CPUs allocated rather than the 4 I requested. Their reason is that the VM performs better with 2 CPUs rather than 4 (according to them). The rationale is that the VM ...
56
votes
8answers
118k 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 ...
56
votes
3answers
13k views

Can I create a top level TLD? (.michael for instance)

It appears that ICANN is allowing the creation of top level domains. Instead of 'registering' a domain, you would essentially be signing up to be a registrar (you'd be giving out registrations on ...
55
votes
11answers
88k views

IIS 7.5 (Windows 7) - HTTP Error 401.3 - Unauthorized

I'm trying to test my ASP.Net website on localhost and I'm getting this error: HTTP Error 401.3 - Unauthorized You do not have permission to view this directory or page because of the access control ...
55
votes
2answers
4k views

How should an IT department choose a standard Linux distribution?

There is a lot of community feeling about what Linux distributions are appropriate for production server environments and which aren't, however, a lot of this feeling seems religiously based, and ...
55
votes
5answers
49k views

How to run a command multiple times?

Is there a way to run a command (e.g. ps aux|grep someprocess) for n times? Something like: run -n 10 'ps aux|grep someprocess' I want to use it interactively, please do not post scripts. ...
55
votes
4answers
26k views

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

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 ...
55
votes
14answers
2k views

Is UPS worthwhile for non-production equipment? [closed]

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 ...
55
votes
10answers
16k views

Unique Features of bash compared to zsh

I have been a zsh user for quite some time (before that tcsh and before that csh). I am quite happy with it, but was wondering if there are any compelling features of bash that do not exist in zsh. ...
55
votes
1answer
63k views

InnoDB: Error: log file ./ib_logfile0 is of different size

I just added the following lines in /etc/mysql/my.cnf after I converted one database to use InnoDB engine. innodb_buffer_pool_size = 2560M innodb_log_file_size = 256M innodb_log_buffer_size = 8M ...
54
votes
15answers
8k 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 ...
54
votes
22answers
81k views

How to copy a large number of files quickly between two servers

I need to transfer a huge amount of mp3s between two serves (Ubuntu). By huge I mean about a million files which are on average 300K. I tried with scp but it would have taken about a week. (about 500 ...
54
votes
1answer
13k views

Why do I need Nginx and something like Gunicorn?

Im looking for a overly simplified answer for the following question. Im trying to build a foundational understanding of how Nginx works along side something like GUnicorn. Do I need both Nginx and ...
54
votes
6answers
101k 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?
54
votes
2answers
67k 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 ...
54
votes
6answers
12k views

Heartbleed: are services other than HTTPS affected?

The OpenSSL 'heartbleed' vulnerability (CVE-2014-0160) affects webservers serving HTTPS. Other services also use OpenSSL. Are these services also vulnerable to heartbleed-like data leakage? I'm ...
54
votes
2answers
335k views

How to check if a port is blocked on a Windows machine?

On the Windows platform, what native options to I have to check if a port (3306, for example) on my local machine (as in localhost), is being blocked?
54
votes
13answers
83k views

Windows 2008: WinSXS directory growing uncontrollably, blocking server

I run a (remotely hosted) virtual Server with Windows 2008 Server for a client. Initially, it had 10 GB of space. During the course of a few weeks - during which nothing was done on the machine ...

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