36
votes
9answers
23k 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 ...
14
votes
4answers
40k 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 ...
36
votes
5answers
66k views

What is the difference between SAN, NAS and DAS?

What is the difference between SAN, NAS and DAS?
41
votes
14answers
6k 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.
28
votes
2answers
44k 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 ...
27
votes
6answers
19k 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?
25
votes
5answers
33k 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 ...
48
votes
8answers
4k 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 ...
46
votes
6answers
55k 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 ...
59
votes
8answers
67k 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?
42
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 ...
29
votes
2answers
10k 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
36k 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 ...
18
votes
5answers
13k 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 ...
14
votes
4answers
21k views

How to make Postfix use another IP address?

I'm using the Postfix mail server and I have 6 IPs available. I'd like to use another IP for the Postfix mail server for sending mail than the web server uses. How can I do this? My postfix version ...
9
votes
9answers
30k views

How to repair/restore ubuntu 10.04 after 'sudo chmod / 777'

See Also: Why is “chmod -R 777 /” destructive? I changed file permissions recursively on the root directory / by executing sudo chmod -R / 777, and after that my system won't ...
17
votes
8answers
23k 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?
13
votes
4answers
892 views

How to schedule server jobs more intelligently than with cron?

I run a job every minute to reindex my site's content. Today, the search engine died, and when I logged in there were hundreds of orphan processes that had been started by cron. Is there another ...
23
votes
2answers
945 views

How do I set up a “secure” open resolver?

This is a Canonical Question about securing public DNS resolvers Open DNS servers seem pretty neat and convenient, as they provide IP addresses that we can use consistently across our company ...
4
votes
3answers
8k 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% / ...
25
votes
9answers
95k 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
4k 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, ...
2
votes
1answer
79 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 ...
88
votes
21answers
18k 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 ...
50
votes
21answers
29k 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 ...
61
votes
5answers
19k views

Active Directory explained

If you had to explain Active Directory to someone how would you explain it?
101
votes
7answers
85k 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 ...
65
votes
11answers
18k 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 ...
50
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 ...
56
votes
15answers
10k 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 ...
49
votes
7answers
37k 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 ...
22
votes
2answers
61k views

How does ServerName and ServerAlias work?

It's the following part of a virtual host config that I need further clarification on: <VirtualHost *:80> # Admin email, Server Name (domain name), and any aliases ServerAdmin ...
33
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 ...
18
votes
7answers
32k views

Force local IP traffic to an external interface

I have a machine with several interfaces that I can configure as I want, for instance: eth1: 192.168.1.1 eth2: 192.168.2.2 I would like to forward all the traffic sent to one of these local ...
40
votes
1answer
11k 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 ...
61
votes
6answers
50k 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?
38
votes
6answers
9k views

If a Windows shop moves “everything” to the cloud, does it still need Active Directory?

Taking a spin off of this question: Do I really need MS Active Directory? in a new direction for 2014. Taking into account a basic Windows infrastructure: domain controllers Exchange 2007/2010/2013 ...
30
votes
3answers
32k views

iptables port redirect not working for localhost

I want to redirect all traffic from port 443 to the internal port 8080. I'm using this config for iptables: iptables -t nat -I PREROUTING --source 0/0 --destination 0/0 -p tcp \ --dport 443 ...
27
votes
8answers
7k views

How do you setup ssh to authenticate using keys instead of a username / password?

How do you setup ssh to authenticate a user using keys instead of a username / password?
22
votes
7answers
27k views

How to workaround the NTFS Move/Copy design flaw?

As anyone that has dealt with file server permissions is aware, NTFS has an interesting design feature/flaw known as the Move/Copy problem. As explained in this MS KB article, the permissions for a ...
21
votes
6answers
6k views

Can windows domain controller be virtualized?

Just the question on the title. There is any problem? Any experience on this?
19
votes
10answers
36k views

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

what would be a command to run in different distros?
46
votes
2answers
13k views

Why does Heroku warn against “naked” domain names?

I ran across this page in the Heroku docs... Naked domains, also called bare or apex domains, are configured in DNS via A-records and have serious availability implications when used in highly ...
17
votes
5answers
12k views

Possible to get SSD TRIM (discard) working on ext4 + LVM + software RAID in Linux?

We use RAID1+0 with md on Linux (currently 2.6.37) to create an md device, then use LVM to provide volume management on top of the device, and then use ext4 as our filesystem on the LVM volume groups. ...
10
votes
5answers
5k views

Is it worth the effort to block failed login attempts

Is it worthwhile running fail2ban, sshdfilter or similar tools, which blacklist IP addresses which attempt and fail to login? I've seen it argued that this is security theatre on a "properly ...
7
votes
3answers
7k 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
5answers
1k views

What's needed for a complete backup system?

For my new server, I want to setup a proper backup solution. I've found a great setup that will do twice-daily incremental backups via Dropbox. I plan on backing up my various databases, the webroot ...
12
votes
3answers
2k views

Apache: Scammers point dozens of domain names at my dedicated IP. How to prevent this?

For the sake of discussion, pretend that I have an Apache webserver which serves a website at www.example.org. This domain name resolves to the public IP address at 192.168.1.100 (pretend this is a ...
19
votes
2answers
2k views

Do the SSH or FTP protocols tell the server to which domain I am trying to connect?

When using the ssh or ftp commands from the Bash shell, does the server that I am connecting to learn of the domain name used? I understand that the domain name is locally translated into an IP ...

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