74
votes
7answers
101k 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
6answers
53k 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 ...
73
votes
17answers
32k 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 ...
73
votes
3answers
41k 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 ...
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
5answers
141k 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 ...
72
votes
7answers
124k 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.
72
votes
1answer
49k 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
17k 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
5answers
199k 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 ...
72
votes
2answers
110k 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
9answers
15k 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
6answers
70k 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. ...
71
votes
6answers
55k 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
23answers
26k 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 ...
71
votes
8answers
97k 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 ...
70
votes
6answers
252k 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<??@@ ...
70
votes
6answers
306k 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 ...
70
votes
1answer
84k 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 ...
69
votes
10answers
181k 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.
69
votes
6answers
152k 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?
69
votes
9answers
178k 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 ...
69
votes
11answers
10k views

Transfer 15TB of tiny files

I'm archiving data from one server to another. Initially I started a rsync job. It took 2 weeks for it to build the file list just for 5 TB of data and another week to transfer 1 TB of data. Then I ...
69
votes
10answers
80k 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 ...
68
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 ...
68
votes
15answers
12k views

Hundreds of failed ssh logins

Every night I get hundreds, sometimes thousands, of failed ssh logins on my RedHat 4 server. For firewall reasons from remote sites, I need to run on the standard port. Is there anything I should be ...
68
votes
20answers
30k 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. ...
67
votes
13answers
43k views

How Often Do Windows Servers Need to be Restarted?

A little background: We have several Windows servers (2003, 2008) for our department. We're a division of IT so we manage our own servers. Of the four of us here I'm the only one with a slight amount ...
67
votes
11answers
71k views

apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName

I keep getting this warning when I (re)start Apache. * Restarting web server apache2 apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ...
67
votes
13answers
28k 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.
66
votes
5answers
59k 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 ...
66
votes
10answers
54k 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 ...
66
votes
6answers
123k 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?
66
votes
8answers
141k 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 ...
66
votes
4answers
57k views

Disable caching when serving static files with Nginx (for development)

We are using Nginx to serve static files on a development platform. As it is a development platform, we'd like to disable caching so that each change is propagated to the server. The configuration of ...
65
votes
4answers
94k 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 ...
65
votes
3answers
8k views

Is it possible to reboot a Linux OS without rebooting the hardware?

Is there a way to reboot a Linux system (Debian in particular) without rebooting the hardware? I have a RAID controller that takes a bit to get itself running before the OS starts up, and I would ...
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 ...
64
votes
6answers
495k 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 ...
64
votes
3answers
28k views

How to re-order windows, change the scroll shortcut, and modify the status bar contents in GNU Screen?

I learned to use gnu-screen and have been using it for the past several weeks. I got a grip of the basics now, and would be very helpful if I get these queries clarified: How do I rename / reorder / ...
63
votes
11answers
20k 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. ...
63
votes
10answers
84k 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 ...
63
votes
23answers
100k 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 ...
63
votes
19answers
19k views

The perfect server room?

What do I have to consider when I'm planning a new server room for a small company (30 PCs, 5 servers, a couple of switches, routers, UPS...)? What are the most important aspects in order to protect ...
63
votes
10answers
88k views

How to tell if a Linux system is big endian or little endian?

I know that certain processors are Big Endian and others are Little Endian. But is there a command, bash script, python script or series of commands that can be used at the command line to determine ...
63
votes
4answers
82k views

Running Cron every 2 hours [duplicate]

I have the cron job as shown below, and wanted it to run every 2 hours, but it keeps running every 2 minutes. Can someone tell me where I'm going wrong? * */2 * * * /path-to-script
63
votes
13answers
170k views

Using wget to recursively download whole FTP directories

I want to copy all of the files and folders from one host to another. The files on the old host sit at /var/www/html and I only have FTP access to that server, and I can't TAR all the files. Regular ...
63
votes
4answers
33k 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 ...
63
votes
11answers
265k 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 ...
63
votes
7answers
105k views

Apache 2 startup warning: NameVirtualHost *:80 has no VirtualHosts

When my Ubuntu Apache server (Apache 2) starts up I get a warning message that reads: [warn] NameVirtualHost *:80 has no VirtualHosts However, the web server is working fine. What might I have ...

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