67
votes
6answers
46k 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?
67
votes
8answers
7k 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+ ...
67
votes
6answers
134k views

Boot and Install Windows from a USB thumb drive

Installing Windows from a thumb drive is vastly superior to burning a copy to a DVD which will fill some landfill somewhere with toxic stuff. Not to mention it's about 50x faster to install Windows ...
66
votes
9answers
33k views

Environment variables of a running process on Unix?

This is to troubleshoot some problems related to environment variables .. On Windows, I could do this by using tool such as ProcessExplorer to select particular process and view values of each ...
66
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 ...
66
votes
4answers
68k views

how to download the ssl certificate from a website?

I want to download the ssl certificate from, say https://www.google.com, using wget or any other commands. Any unix command line? wget or openssl?
65
votes
13answers
32k views

What steps do you take to secure a Debian server?

I am installing a Debian server which is connected directly to the Internet. Obviously I want to make it as secure as possible. I would like you guys/gals to add your ideas to secure it and what ...
65
votes
1answer
9k 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?
65
votes
1answer
40k views

What is a challenge password?

I'm setting up SSL on an Ubuntu server. One of fields it asks for as part of setting up the CSR is a "challenge password". What is that? The default is blank. Do I need to enter one?
65
votes
8answers
7k views

How can a single disk in a hardware SATA RAID-10 array bring the entire array to a screeching halt?

Prelude: I'm a code-monkey that's increasingly taken on SysAdmin duties for my small company. My code is our product, and increasingly we provide the same app as SaaS. About 18 months ago I moved ...
64
votes
9answers
10k 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?
64
votes
13answers
14k views

Are networks now faster than disks?

This is a software design question I used to work on the following rule for speed cache memory > memory > disk > network With each step being 5-10 times the previous step (e.g. cache ...
63
votes
13answers
66k views

How to reconnect to a disconnected ssh session

Is there a way to connect to an ssh session that was disconnected? We are having problems with our network connection to a remote site that we are working on separately; however, in the mean time we ...
62
votes
9answers
59k views

Shell command to monitor changes in a file - What's it called again?

I know there was a command on Unix that I could use to monitor a file and see changes that are getting written to it. This was quite useful especially for checking log files. Do you know what it is ...
62
votes
7answers
81k views

How to forcibly close a socket in TIME_WAIT?

I run a particular program on linux which sometimes crashes. If you open it quickly after that, it listens on socket 49201 instead of 49200 as it did the first time. netstat reveals that 49200 is in ...
62
votes
9answers
74k views

When does `cron.daily` run?

When do entries in cron.daily (and .weekly and .hourly) run, and is it configurable? I haven't found a definitive answer to this, and am hoping there is one. I'm running RHEL5 and CentOS 4, but for ...
62
votes
9answers
158k 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 ...
62
votes
10answers
95k views

How do you add a Windows environment variable without rebooting?

This is probably an easy answer, but I have never been able to find it by googling. I simply would like to add an Environment variable to a Windows machine (desktop or server) and be able to use it ...
62
votes
11answers
66k 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 ...
62
votes
8answers
24k views

ssh-agent forwarding and sudo to another user

If I have a server A into which I can login with my ssh key and I have the ability to "sudo su - otheruser", I lose key forwarding, because the env variables are removed and the socket is only ...
62
votes
9answers
69k 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 ...
61
votes
6answers
3k views

Choosing between meaningful and meaningless hostnames

Assume an environment with a puppet-managed cluster of different servers - various hardware, software, operating systems, virtual/dedicated, etc. Would you choose meaningful hostnames ...
60
votes
15answers
9k 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 ...
60
votes
2answers
84k 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 ...
59
votes
13answers
30k 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 ...
59
votes
19answers
17k 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 ...
59
votes
6answers
54k views

Can I automatically add a new host to known_hosts?

Here's my situation; I'm setting up a test harness that will, from a central client, launch a number of virtual machine instances and then execute commands on them via SSH. The virtual machines will ...
59
votes
5answers
9k 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?
59
votes
14answers
33k views

64-bit TortoiseSVN on Windows 7 says “file or directory is corrupted and unreadable” then runs chkdsk

I'm using 64-bit TortoiseSVN on a 64-bit Windows 7 Professional. Every so often a checkout or update will fail with an error message like the following. Error: Can't move Error: ...
59
votes
11answers
58k views

How to know from which yum repository a package has been installed

After I have installed a package by yum (with multiple repository configured), how can I found from which repository it has been installed? If I run yum info package name (or yum list package name), I ...
58
votes
2answers
9k views

Can you help me with my capacity planning?

This is a Canonical Question about Capacity Planning Related: How do you do Load Testing and Capacity Planning for Web Sites? How do you do Load Testing and Capacity Planning for ...
57
votes
13answers
25k views

Why is RAID not a backup?

When someone mentions RAID in a conversation about backups, invariably someone declares that "RAID is not a backup." Sure, for striping, that's true. But what's the difference between redundancy and ...
57
votes
8answers
109k views

What version of RHEL am I using?

How can I determine from the shell with no privileges what the Red Hat Enterprise Linux version is, for example is it RHEL 4 or RHEL 5.1?
57
votes
7answers
5k views

DNS failing to propagate worldwide

I haven't changed anything related to the DNS entry for serverfault.com, but some users were reporting today that the serverfault.com DNS fails to resolve for them. I ran a justping query and I can ...
57
votes
7answers
97k 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 ...
57
votes
2answers
46k views

how to disable SSH login with password for some users?

On Linux (Debian Squeeze) I would like to disable SSH login using password to some users (selected group or all users except root). But I do not want to disable login using certificate for them. ...
56
votes
14answers
34k views

Top level domain for private networks?

On our office network we have an internal DNS and all the hostnames are whatever.lan. On my VMware VMs, on their host-only network I call them whatever.vm. We now have a private IP space network in ...
56
votes
10answers
43k 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 ...
56
votes
3answers
51k views

Meaning of the buffers/cache line in the output of free

Why does my server show total used free shared buffers cached Mem: 12286456 11715372 571084 0 81912 6545228 -/+ buffers/cache: 5088232 7198224 ...
56
votes
3answers
70k 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?
56
votes
7answers
46k 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 ...
56
votes
11answers
85k views

Subversion error: (405 Method Not Allowed) in response to MKCOL

I am getting the following error while trying to commit a new directory addition. svn: Commit failed (details follow): svn: Server sent unexpected return value (405 Method Not Allowed) in response to ...
55
votes
22answers
9k views

How the heck is http://to./ a valid domain name?

Apparently it's a URL shortener. It resolves just fine in Chrome and Firefox. How is this a valid top-level domain? Update: for the people saying it's browser shenanigans, why is it that: ...
55
votes
9answers
40k 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 ...
55
votes
10answers
39k views

How can I get the size of an Amazon S3 bucket?

I'd like to graph the size (in bytes, and # of items) of an Amazon S3 bucket and am looking for an efficient way to get the data. The s3cmd tools provide a way to get the total file size using s3cmd ...
55
votes
7answers
194k 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 ...
55
votes
2answers
12k views

Amazon EC2 terminology - AMI vs. EBS vs. Snapshot vs. Volume

I have been poking around Amazon EC2, and am a little confused on some of the terminology. Specifically with regard to AMI, snapshots and volumes, and an EBS Please correct me if I am wrong, or fill ...
55
votes
3answers
12k views

How do you do load testing and capacity planning for web sites?

This is a canonical question about capacity planning for web sites. Related: Can you help me with my capacity planning? How do you do Load Testing and Capacity Planning for ...
54
votes
9answers
329k views

Command line to list users in a Windows Active Directory group?

Is there a command line way to list all the users in a particular Active Directory group? I can see who is in the group by going to Manage Computer --> Local User / Groups --> Groups and double ...
54
votes
10answers
3k views

How to extinguish a small fire in a server rack to minimize damage to surrounding equipment?

Suppose I have a rack with several servers and other stuff. One of servers overheats severely and either starts smoking or catches fire while there's a serviceman nearby. If anything similar happens ...

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