80
votes
6answers
41k 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 ...
80
votes
3answers
167k views

How to sleep in a batch file?

How to pause execution for a while in a Windows batch file between a command and the next one?
80
votes
4answers
39k 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?
80
votes
8answers
40k views

Heartbleed: how to reliably and portably check the OpenSSL version?

I was looking at a reliable and portable way to check the OpenSSL version on GNU/Linux and other systems, so users can easily discover if they should upgrade their SSL because of the Heartbleed bug. ...
80
votes
4answers
15k views

Why is TCP accept() performance so bad under Xen?

The rate at which my server can accept() new incoming TCP connections is really bad under Xen. The same test on bare metal hardware shows 3-5x speed ups. How come this is so bad under Xen? Can you ...
79
votes
10answers
48k views

How to create a UUID in bash?

In Java it is possible to create a random UUID: UUID uuid = UUID.randomUUID(); How to do this in Bash?
79
votes
2answers
82k 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 ...
79
votes
3answers
118k 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?
78
votes
16answers
8k views

How dangerous is a wet server room floor

We have a couple of tower servers in a small server room. The carpet is wet as a result of the cooler and no-one else really seems concerned about this but I'm not too happy. I'm only a lowly ...
78
votes
17answers
33k 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 ...
78
votes
17answers
49k views

Should network hardware be set to “autonegotiate” speeds or fixed speeds?

We recently had a little problem with networking where multiple servers would intermittently lose network connectivity in a fairly painful-to-resolve way (required hard reboot). This has been going on ...
78
votes
5answers
98k 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 ...
78
votes
9answers
61k 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 ...
78
votes
5answers
13k 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?
77
votes
3answers
103k 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 ...
77
votes
4answers
175k 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
77
votes
8answers
83k views

How much network latency is “typical” for east - west coast USA?

At the moment we're trying to decide whether to move our datacenter from the west coast to the east coast. However, I am seeing some disturbing latency numbers from my west coast location to the east ...
77
votes
5answers
151k views

How to start/stop/restart launchd services from the command line?

How do I restart, say for example my httpd or afpd, running any Mac OS X >= 10.5 (Leopard-), without having to use the GUI and go to System Preferences -> Sharing and unchecking/checking "Web Sharing"?...
77
votes
2answers
101k 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 ...
76
votes
5answers
9k views

How do I protect my company from my IT guy? [closed]

I'm going to hire an IT guy to help manage my office's computers and network. We're a small shop, so he'll be the only one doing IT. Of course, I'll interview carefully, check references, and run a ...
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 ...
75
votes
11answers
199k views

How do you restart php-fpm?

I need to reload my php.ini and there's nothing in the help dialog about restarting it.
75
votes
6answers
55k 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 ...
75
votes
3answers
44k views

How does IPv6 subnetting work and how does it differ from IPv4 subnetting?

This is a Canonical Question about IPv6 Subnetting. Related: How does IPv4 Subnetting Work? I know a lot about IPv4 Subnetting, and as I prepare to (deploy|work on) an IPv6 network I ...
75
votes
8answers
12k views

How to backup 20+TB of data?

We have a NAS server at the company I work for that is being used for storing photography sessions. Each session is approximately 100gb. Over the last couple of years this server has accumulated 10+ ...
75
votes
5answers
207k 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....
74
votes
7answers
103k 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. ...
74
votes
7answers
133k 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.
73
votes
6answers
161k views

Find name of Active Directory domain controller

How can I find out the name/IP address of the AD domain controller on my network?
73
votes
14answers
5k views

What's wrong with always being root?

I have a feeling this is a stupid question, but this is something I've wondered for awhile. I have a VPS and this is my first big linux venture. I am the only person who has access to it. My question ...
73
votes
8answers
104k views

How do I find the UUID of a filesystem

I'm running Ubuntu, and want to find out the UUID of a particular filesystem (not partition). I know I can use e2label /dev/sda1 to find out the filesystem label, but there doesn't seem to be a ...
72
votes
6answers
74k 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. Update:...
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 ...
72
votes
6answers
323k 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 ...
72
votes
1answer
53k views

SSH use only my password, Ignore my ssh key, don't prompt me for a passphrase

This is a question regarding the OpenSSH client on Linux, MacOSX and FreeBSD. Normally, I log into systems using my SSH key. Occasionally, I want my SSH client to ignore my SSH key and use a ...
72
votes
1answer
18k views

What happens when you plug two sides of a cable to a single networking device?

What is likely to happen when you plug two ends of a network cable to a single switch/router? Will this create problems on the network, or just be ignored?
72
votes
17answers
13k views

Does orientation affect hard drive lifespan?

Are there any studies or evidence which show that mounting a hard drive horizontally is better than vertically for the lifespan of the device? Or upside down, or any direction for that matter.
72
votes
2answers
113k views

How to Configure Windows Machine to Allow File Sharing with DNS Alias

What process is necessary to configure a Windows environement to allow me to use DNS CNAME to reference servers? I want to do this so that I can name my servers something like SRV001, but still have \...
71
votes
86answers
7k views

What are your favorite open source tools?

I believe every system administrator is used to open source by now. From Apache to Firefox or Linux, everyone uses it at least a little bit. However, most open source developers are not good in ...
71
votes
9answers
16k views

Linux - Is there a way to prevent/protect a file from being deleted even by root?

I have a very important file which an application in my workplace uses, i need to make sure it is not delete whatsoever, how can I do that?
71
votes
11answers
202k views

How to mount a CD/DVD ISO in Windows 7?

Does Windows 7 have native support for mounting CD/DVD ISO images? If not, what is the best tool to use for that under Windows 7 64-bit? I am looking for a solution to allow installing MSDN ...
71
votes
6answers
56k views

How to test if my server is vulnerable to the ShellShock bug?

How can I ensure my Bash installation is not vulnerable to the ShellShock bug anymore after the updates?
71
votes
1answer
88k 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 ...
70
votes
4answers
99k views

How can I see Time-To-Live (TTL) for a DNS record?

I would like to see the Time-To-Live (TTL) value for a CNAME record. I have access to dig (on Apple Mac OS X), which gives me an answer like this: % dig host.example.gov <*SNIP*> ;; ANSWER ...
70
votes
6answers
266k views

How can I read pcap files in a friendly format?

a simple cat on the pcap file looks terrible: $cat tcp_dump.pcap ?ò????YVJ? JJ ?@@.?E<??@@ ?CA??qe?U????иh? .Ceh?YVJ?? JJ ?@@.?E<??@@ CA??qe?U????еz?...
70
votes
12answers
7k views

Exchange server replacement that runs on Linux

I've worked as a sysadmin for some years and what I keep coming back to is that users like Microsoft Outlook and want to use its Exchange features. I have tried my fair share of commercial ...
70
votes
10answers
81k views

Dealing with HTTP w00tw00t attacks

I have a server with apache and I recently installed mod_security2 because I get attacked a lot by this: My apache version is apache v2.2.3 and I use mod_security2.c This were the entries from the ...
69
votes
5answers
62k views

“POSSIBLE BREAK-IN ATTEMPT!” in /var/log/secure — what does this mean?

I've got a CentOS 5.x box running on a VPS platform. My VPS host misinterpreted a support inquiry I had about connectivity and effectively flushed some iptables rules. This resulted in ssh listening ...
69
votes
20answers
31k 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. ...
69
votes
9answers
179k views

Can't seem to disable Java Automatic Update

I'm just tweaking out my new Windows 7 laptop and wanted to disable the automatic Java updating (and thus kill the silly jusched.exe background process), but I can't seem to get it to actually turn it ...

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