54
votes
5answers
15k views

Active Directory explained

If you had to explain Active Directory to someone how would you explain it?
53
votes
3answers
15k 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 ...
54
votes
11answers
15k 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 ...
120
votes
12answers
10k views

Should servers be turned off at night?

There is a server that is used from 4:30 am in the morning until ~ 22:00. Should it be turned off? I think that it is a server and that it won't have a problem to stay on, but serious professors are ...
52
votes
11answers
108k 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" ...
40
votes
2answers
2k views

vSphere education - What are the downsides of configuring VMs with *too* much RAM?

VMware memory management seems to be a tricky balancing act. With cluster RAM, Resource Pools, VMware's management techniques (TPS, ballooning, host swapping), in-guest RAM utilization, swapping, ...
92
votes
4answers
13k views

Should I quit using Ifconfig?

With the servers that mount Infiniband cards, when I use the ifconfig command, I get this warning: Ifconfig uses the ioctl access method to get the full address information, which limits hardware ...
34
votes
16answers
30k views

Is Round-Robin DNS “good enough” for load balancing static content?

We have a set of shared, static content that we serve up between our websites at http://sstatic.net. Unfortunately, this content is not currently load balanced at all -- it's served from a single ...
53
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 ...
17
votes
6answers
10k views

MySQL InnoDB - innodb_file_per_table cons?

By default MySQL InnoDB stores all tables of all DBs in one global file. You can change this by setting innodb_file_per_table in the config, which then creates one data file for each table. I am ...
44
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 ...
30
votes
1answer
6k views

Why are my XFS filesystems suddenly consuming more space and full of sparse files?

I've run XFS filesystems as data/growth partitions for nearly 10 years across various Linux servers. I've noticed a strange phenomenon with recent CentOS/RHEL servers running version 6.2+. Stable ...
28
votes
6answers
8k views

Meaning of directories on Unix and Unix like systems

I've been using Linux for a couple of years now but I still haven't figured out what the origin or meaning of some the directory names are on Unix and Unix like systems. E.g. what does etc stand for ...
24
votes
5answers
32k views

What is the difference between SAN, NAS and DAS?

What is the difference between SAN, NAS and DAS?
14
votes
3answers
19k views

how i can identify which process is making UDP traffic on linux?

my machine is continously making udp dns traffic request. what i need to know is the PID of the process generating this traffic. The normal way in TCP connection is to use netstat/lsof and get the ...
25
votes
13answers
3k views

Server Hosting from your House - $200 to $300 per month range

I'm a developer lacking some infrastructure knowledge. What is the fattest pipe I can get to my house in the $200 to $300 range? I'd like to host a few servers at my house. Then if my company gets ...
24
votes
7answers
33k views

Apache Default/Catch-All Virtual Host?

If I have 3 domains, domain1.com, domain2.com, and domain3.com, is it possible to set up a default virtual host to domains not listed? For example, if I would have: <VirtualHost 192.168.1.2 ...
19
votes
5answers
4k views

Unix Server Partitioning & Filesystem Layout

There's a lot of contradictory information about Unix server partitioning out on the internet, so I need some advice on how to proceed. So far, on the servers I in our test environment I didn't ...
47
votes
8answers
46k views

Is a wildcard CNAME DNS record valid?

I know it's valid to have a DNS A record that's a wildcard (e.g. *.mysite.com). Is it possible/valid/advised to have a wildcard CNAME record?
44
votes
6answers
34k views

Is X.Y.Z.0 a valid IP address?

Are IP addresses with a 0 in the last octet valid? 10.6.43.0 In my case, I have the the following netmask 255.255.252.0 What about a 0 for the other octets?
23
votes
8answers
25k views

Will disabling hyperthreading improve performance on our SQL Server install

Related to: Current wisdom on SQL Server and Hyperthreading Recently we upgraded our Windows 2008 R2 database server from an X5470 to a X5560. The theory is both CPUs have very similar performance, ...
14
votes
10answers
26k views

How do I know if I am running 32 or 64-bit Linux?

what would be a command to run in different distros?
26
votes
8answers
22k views

Private IP address in public DNS

We have an SMTP only mail server behind a firewall which will have a public A record of mail.. The only way to access this mail server is from another server behind the same firewall. We do not run ...
12
votes
5answers
61k views

Huge amount of TIME_WAIT connections says netstat

Okay, this is creeping me out - I see about 1500-2500 of these: root@wherever:# netstat Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 ...
11
votes
6answers
11k views

How can I determine what is taking up so much space?

I was using df -h to print out human readable disk usage. I would like to figure out what is taking up so much space. For instance, is there a way to pipe this command so that it prints out files that ...
16
votes
12answers
41k views

How do I know if I'm working on a Virtual Machine or not?

Is there a way to know if the Windows machine I'm working on is virtual or physical? (I'm connecting with RDP to the machine. If it's a virtual machine it is working and handled by VMWare).
10
votes
2answers
6k views

SSL site not using the correct IP in Apache and Ubuntu

I'm trying to set up an apache-ubuntu-php webserver. My webserver will host multiple SSL sites, each SSL site will have it's own IP address (unless there's a better way to do this). So I suppose the ...
14
votes
7answers
15k views

How to change “From:” field for emails from Cron?

I use remote SMTP via nullmailer and it requires set From field to the specific name, but cron set it as root@my.sweet.server.com. How could I change it to something like me@ya.ru?
6
votes
4answers
2k views

Rotate logs of a dumb non-interactive application

Ubuntu 10.4 Server. I have a dumb non-interactive legacy service which is running constantly on my server. It is writing its log to a file with fixed name (/var/log/something.log). It does not ...
4
votes
3answers
5k views

How to diagnose causes of oom-killer killing processes

I have a small virtual private server running CentOS and www/mail/db, which has recently had a couple of incidents where the web server and ssh became unresponsive. Looking at the logs, I saw that ...
2
votes
1answer
1k views

Setting up a Rails 2.3.x app on EC2 for easy scalability

I'm running a simple rails stack on a single dedicated machine. We're reaching our full capacity and have absolutely no setup for scaling, just one app on one machine. I did some research and came up ...
12
votes
5answers
4k views

ZFS best practices with hardware RAID

If one happens to have some server-grade hardware at ones disposal, is it ever advisable to run ZFS on top of a hardware-based RAID1 or some such? Should one turn off the hardware-based RAID, and run ...
11
votes
9answers
28k views

NRPE unable to read output, but why?

I have this problem with NRPE, all the stuff I've found so far on the net seems to point me at things I've already tried. # /usr/local/nagios/plugins/check_nrpe -H nrpeclient gives NRPE v2.12 as ...
5
votes
6answers
25k views

Windows Event Log - email notification

Is there an easy way to send an email when a particular severity of event from a particular service hits the Windows server event log? This is on Windows Server 2003, if it makes a difference. n.b. ...
4
votes
5answers
2k views

Deep Format of a Harddrive on a Linux System

I've got an original Asus Eee PC Netbook that I'd like to sell. When I've sold old computers in the past, I've typically done a deep/secure/zeroing out style format. How can I do this on a Linux ...
17
votes
2answers
4k views

Is dig +trace always accurate?

When the accuracy of a DNS cache is in question, dig +trace tends to be the recommended way of determining the authoritative answer for an internet facing DNS record. This seems to be particularly ...
3
votes
3answers
4k views

simple rsync in crontab without password

I would like to run the following: (Centos 5.4) rsync -avz /source_folder 192.168.1.1:/destination_folder right now I'm running it from CLI but eventually I would like to run it from crontab ...
6
votes
2answers
1k views

SQL Server memory constantly going up, from 1GB RAM used to 7GB in a week

I have a ~45GB database that increases rapidly (~1GB every week). So it's doing a lot of inserts; the web app doesn't have many users so reads are low right now. But I'm noticing that the RAM sql ...
3
votes
3answers
27k views

chmod -R 777 / on ubuntu - numerous problems

A client has accidentally given the entire filesystem full permissions on their ubuntu 10.04 box. chmod -R 777 httpdocs/cd / As you can see they attempted to cd to the root, and instead gave chmod ...
2
votes
1answer
709 views

Server refuses to use swap partition

We are running a server with 23 cores (cpuinfo shows 22 as the highest process number) and 66 Gig RAM. The development team here is running some apps, which hogs memory. I have observered that: 1. ...
2
votes
2answers
876 views

What do I need to parse incoming emails?

My intention is to parse incoming emails with PHP. What would be the simplest way to set this up? Would it suffice to rely on Postfix for this, or is there a better alternative? The purpose of the ...
15
votes
6answers
54k views

How can an unauthenticated user access a windows share?

I have a directory shared on my computer, which is part of the domain. Is it possible to set up the share so that a user logged on to a different machine which is not part of the domain can access my ...
4
votes
2answers
1k views

3rd party SSD drive in HP Proliant server only shows 3G transfer speed

After receiving some excellent advice in a previous question, we've bought a OWC Mercury Extreme Pro drive for use in our HP Proliant DL360 G7 server. Both the drive, and the P410i array controller, ...
4
votes
2answers
288 views

Accidential CHMOD 755

Alright, I accidentially chomdded everything to 755, which isn't as terrible as chowning everything to the local user. How insecure is this and how would I restore it easily, without reinstalling?
3
votes
3answers
2k views

What is the memory module on a RAID card needed for?

As above, what is the reason for needing a memory module on a RAID card? The card I am looking at (HP P410) comes with either 256MB or 512MB but unsure which to get and why.
1
vote
2answers
644 views

revert chmod 777 / -R

while executing a command i made a mistake and executed (ubuntu 10) sudo chmod 777 / -R # okay you may laugh now all my filesystem has 777 permitions , obviously i dont know which ...
-3
votes
1answer
1k views

How do I open custom ports in my iptables firewall? [closed]

I need IPTables, like everyone else, but I don't use it enough to really keep my knowledge complete and fresh. The setup utility in CentOS is too basic. It doesn't seem to allow me to open up custom ...
76
votes
8answers
170k 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 ...
49
votes
9answers
66k 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 ...
35
votes
20answers
16k views

Storing a million images in the filesystem

I have a project that will generate a huge number of images. Around 1,000,000 for start. They are not large images so I will store them all on one machine at start. How do you recommended on ...

15 30 50 per page