13
votes
3answers
16k 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: ...
26
votes
3answers
19k views

Linux - How can I see what's waiting for disk IO

I have a server that has a really high load. Nothing is jumping out at me in terms of CPU usage, and it's not swapping. I think it's cause some processes are waiting for disk IO, and I want to see ...
29
votes
5answers
10k 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 ...
70
votes
14answers
4k 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 ...
33
votes
5answers
3k views

Smoothest workflow to handle SSH host verification errors?

This is a simple issue that we all face and probably resolve manually without giving much thought. As servers change, are re-provisioned, or IP addresses reallocated, we receive the SSH host ...
26
votes
5answers
3k views

Linux server out of space

I have been asked this question in two consecutive interviews, but after some research and checking with various systems administrators I haven't received a good answer. I am wondering if somebody can ...
21
votes
12answers
41k views

VMware Linux Server — how can you tell if you are a vm or real hardware?

An interesting question. I have logged into a Linux (most likely SuSE) host. Is there some way that I can tell programmatically that I am a VM host or not? Also assume that the vmtools are not ...
20
votes
9answers
14k views

Multiple domains with SSL on same IP

I know that a dedicated IP is needed for setting up SSL. What happens if we add SSL for domains sharing an IP ? (Namevirtualhost)
16
votes
3answers
6k views

Naming a new Active Directory forest - why is split-horizon DNS not recommended?

Hopefully, we all know what the recommendations for naming an Active Directory forest are, and they're pretty simple. Namely, it can be summed up in a single sentence. Use a subdomain of an ...
1
vote
1answer
268 views

Lame DNS server

I'm trying to setup my BIND with a domain I own and I'm using dnssy.com and intodns.com to check if everything is ok, but I'm getting errors in both. The error says that my DNS server is "lame" ...
15
votes
4answers
6k views

How is Windows Server different from regular Windows?

I can run IIS on a normal installation, what is so different about windows server?
2
votes
2answers
4k views

Non-volatile cache RAID controllers: what kind of protection is there against NVCACHE failure?

The battery back-up (BBU) model: admin enables write-back cache with BBU writes are cached to the RAID controller's RAM (major performance benefit) the battery saves uncommitted and cached data in ...
288
votes
21answers
51k views

How do you search for backdoors from the previous IT person?

We all know it happens. A bitter old IT guy leaves a backdoor into the system and network in order to have fun with the new guys and show the company how bad things are without him. I've never ...
113
votes
13answers
114k views

How to set up Nginx as a caching reverse proxy?

I heard recently that Nginx has added caching to its reverse proxy feature. I looked around but couldn't find much info about it. I want to set up Nginx as a caching reverse proxy in front of ...
45
votes
2answers
3k 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, ...
100
votes
4answers
18k 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 ...
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 ...
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 ...
32
votes
16answers
15k views

Linux - Running The Same Command on Many Machines at Once

I have about a dozen Linux boxes that I occasionally need to run the same command(s) on. Is there an easier way (or automated way) to do this asides from logging on to each machine and running the ...
39
votes
15answers
5k views

Preventing brute force attacks against ssh?

What tool or technique do you use to prevent brute force attacks against your ssh port. I noticed in my Security logs, that I have millions of attempts to login as various users through ssh. This is ...
10
votes
3answers
2k views

LAMP Server Performance Tips [closed]

What performance tips can be offered to someone running a LAMP server? In the instance that something is Distribution specific, I'm targeting Debian.
34
votes
9answers
18k views

Why not block ICMP?

I think I almost have my iptables setup complete on my CentOS 5.3 system. Here is my script... # Establish a clean slate iptables -P INPUT ACCEPT iptables -P FORWARD ACCEPT iptables -P OUTPUT ACCEPT ...
11
votes
3answers
29k views

iptables - Target to route packet to specific interface?

My home server has two main interfaces, eth1 (a standard internet connection) and tun0 (an OpenVPN tunnel). I'd like to use iptables to force all packets generated by a local process owned by UID ...
24
votes
2answers
37k views

How to reduce number of sockets in TIME_WAIT?

Ubuntu Server 10.04.1 x86 I've got a machine with a FCGI HTTP service behind nginx, that serves a lot of small HTTP requests to a lot of different clients. (About 230 requests per second in the peak ...
25
votes
6answers
15k views

Log all commands run by admins on production servers

It is company policy for admins to login to the servers via a personal username, and then run sudo -i to become root. Upon running sudo -i, sudo will create an environmental variable called ...
24
votes
6answers
14k views

CIDR for Dummies

I understand what CIDR is, and what it is used for, but I still can't figure out how to calculate it in my head. Can someone give a "for dummies" type explanation with examples?
41
votes
12answers
2k views

Sell partitioning to me

I have often wondered why there is such a passion for partitioning drives, especially on Unixy OSes (/usr, /var, et al). This does not seem to be a common theme with Windows installations. It seems ...
26
votes
7answers
103k views

Finding why a user is locked out in Active Directory

A user's account keeps getting locked out in Active Directory. It's probably caused by an app that's using Windows authentication to connect to SQL Server. Is there a way to find out which app is ...
24
votes
2answers
7k views

SSL password on apache2 restart

I setup wildcard SSL certificate from Godaddy on Apache2. Whenever the server restarts it asks for the passphrase for the SSL certificate's private key. What's the best way to remove this obstacle ...
21
votes
6answers
33k views

Choosing local versus public domain name for Active Directory [duplicate]

What are the pros and cons of choosing a local domain name such as mycompany.local versus a publicly registered domain name such as mycompany.com (assuming that your org has registered the public ...
21
votes
4answers
63k views

How to configure vsftpd to work with passive mode

Whenever I install vsftpd on centos, I only setup the jail environment for the users and rest is default configuration of vsftpd. I create user and try to connect with filezila ftp client but I could ...
18
votes
5answers
12k views

How can I chroot ssh connections?

I would like to setup a chroot jail for most (not all) users logging in though SSH. I've heard it's possible with the latest versions of openssh, but I've not been able to find out how to do it. The ...
15
votes
7answers
15k views

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

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 ...
13
votes
5answers
7k 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 ...
15
votes
4answers
1k views

SSL certificate selection based on host-header: is it possible?

Is it possible for a web server to select an SSL certificate to use based on the host-header of the incoming connection, or is that information that is only available after the SSL connection is ...
26
votes
5answers
10k views

CNAME for top of domain?

Is it possible to set a CNAME record at the top of a domain? (i.e. @ CNAME www, @ CNAME foobar.com., etc.) My ISP says that it's only possible to use CNAME's for subdomains but I've read somewhere ...
3
votes
3answers
5k views

How do I find out what is using up all the space on my / partition?

I am on a large instance on Amazon's EC2 servers. I run the df command and get: root@db:~# df -h Filesystem Size Used Avail Use% Mounted on /dev/sda1 9.9G 9.1G 284M 98% / ...
-1
votes
2answers
1k 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: ...
4
votes
4answers
1k 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 ...
2
votes
1answer
70 views

Hosting multiple distinct folders for distinct domains

I have a VPS that I've installed a Apache Web Server on. What I want to do is forward my own website domains to that server and host those websites' files inside my Apache Web Server. As far as I ...
56
votes
8answers
119k 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 ...
107
votes
9answers
52k views

Keeping a linux process running after I logout

I'm connecting to a Linux machine through SSH, and I'm trying to run a heavy bash script that makes filesystem operations. It's expected to keep running for hours, but I cannot leave the SSH session ...
75
votes
19answers
16k views

Why should I firewall servers?

PLEASE NOTE: I'm not interested in making this into a flame war! I understand that many people have strongly-held beliefs about this subject, in no small part because they've put a lot of effort into ...
62
votes
3answers
24k 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 ...
46
votes
40answers
5k 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 ...
64
votes
5answers
4k views

Choosing between meaningful and meaningless hostnames [closed]

Assume an environment with a puppet-managed cluster of different servers - various hardware, software, operating systems, virtual/dedicated, etc. Would you choose meaningful hostnames ...
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 ...
41
votes
5answers
24k views

Allow SFTP but disallow SSH?

I'm starting a very little hosting company for a few friends and little clients, nothing big. I want to give my "clients" the right to manage their files on the server. I hate FTP as it is not secure ...
36
votes
16answers
36k 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 ...
34
votes
23answers
5k views

Who is a good registrar these days? [closed]

It's been a long time since I've had to register a new domain. What registrar is considered geek and sysadmin friendly? I've heard that godaddy will screw you 10 ways to Sunday, and a lot of the ...

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