Linux is the generic term for a UNIX-like open source operating system based on the Linux kernel.

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Allow SCP but not actual login using SSH

Is there any way to configure a user on a Linux box (Centos 5.2 in this case) so that they can use scp to retrieve files, but can't actually login to the server using SSH?
39
votes
5answers
89k views

How to install/change locale on Debian?

I've written a web application for which the user interface is in Dutch. I use the system's date and time routines to format date strings in the application. However, the date strings that the system ...
38
votes
4answers
67k views

EPEL Repo for CentOS 6 causing error

I've got a VM running CentOS 6 (64bit) and I'm attempting to add the EPEL repo like usual to install various packages as I do quite regularly. Today, I'm experiencing some strange errors yet I'm ...
38
votes
7answers
11k views

Should websites live in /var/ or /usr/ according to recommended usage?

According to a guide on the Linux directory structure, /usr/ is for application files, and /var/ is for files that change (I assume this means "files that belong to the applications"). Is this correct?...
38
votes
6answers
42k views

What is “-bash: !”: event not found"

Try executing the following under a bash shell echo "Reboot your instance!" On my installation: root@domU-12-31-39-04-11-83:/usr/local/bin# bash --version GNU bash, version 4.1.5(1)-release (i686-pc-...
38
votes
8answers
70k views

How to add a timestamp to bash script log?

I have a constantly running script that I output to a log file: script.sh >> /var/log/logfile I'd like to add a timestamp before each line that is appended to the log. Like: Sat Sep 10 21:...
38
votes
7answers
68k views

How to automatically start supervisord on Linux (Ubuntu)

Supervisord does not come with an init script or does not indicate how to get it started automatically, ie. after a reboot. I've tried some user-contributed /etc/init.d scripts, but they all fail. ...
38
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5answers
5k views

Intentionally cause an I/O error in Linux?

Is there anyway, with Linux, to purposely cause a block device to report an I/O error, or possibly simulate one for testing purposes?
38
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8answers
11k views

What tool do you recommend to track changes on a Linux/Unix server

I manage several Linux servers for clients in several roles like email, caching, web serving, filtering, firewalling/routing, and so on. Since I don't own these computers and just provide remote ...
37
votes
4answers
5k views

“reboot” or “shutdown -r now”: what restart command is safer?

We have in our organization around ~500 RedHat Linux machines. On all the machines we installed applications and services under /etc/init.d, and oracle RAC servers. We intend to perform yum updates ...
37
votes
8answers
207k views

How to check the physical status of an ethernet port in Linux?

I want to check if a specified ethX is physically up or down. How do I do that with the command line?
37
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52answers
7k views

Favorite Unix command line aliases? [closed]

What are your favorite command line aliases (bash/sh/tcsh) aliases? Here are a few of mine. alias lsr='ls -lrt' alias gon='cd $HOME/Notes' alias devdb='mysql -h dev --user=x --password=secret ...
37
votes
6answers
46k views

How can I prevent a DDOS attack on Amazon EC2?

One of the servers I use is hosted on the Amazon EC2 cloud. Every few months we appear to have a DDOS attack on this sever. This slows the server down incredibly. After around 30 minutes, and ...
37
votes
6answers
11k views

Can you have more than one ~/.ssh/config file?

We have a bastion server that we use to connect to multiple hosts, and our .ssh/config has grown to over a thousand lines (we have hundreds of hosts that we connect to). This is beginning to get a ...
37
votes
6answers
39k views

How do I list loaded Linux module parameter values?

Is there a standard way to list the parameter values of a loaded Linux module? I'm essentially probing for another answer to this Linux kernel module parameters question, because the module I'm ...
36
votes
9answers
24k 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 ...
36
votes
5answers
13k views

Why does a hardware router perform better than a Linux router with better specs (RAM & CPU)?

I have a minimal CentOS 6.3, 64 bit acting as gateway with 4 NIC (1 Gbps), each bonded together one for public traffic and other for private, which performs NATing. It has 6 GB RAM and 4 logical cores....
36
votes
3answers
4k views

Why is Linux reporting “free” memory strangely?

This is a canonical question about how Unix operating systems report memory usage. Similar Questions: Server refuses to use swap partition Memory Usage in LINUX I have production ...
36
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10answers
5k views

Run antivirus software on linux DNS servers. Does it make sense?

During a recent audit we were requested to install antivirus software on our DNS servers that are running linux (bind9). The servers were not compromised during the penetration testing but this was ...
36
votes
8answers
63k views

How to interrupt software raid resync?

I want to interrupt a running resync operation on a debian squeeze software raid. (This is the regular scheduled compare resync. The raid array is still clean in such a case. Do not confuse this with ...
36
votes
3answers
6k views

Run command in bash without save in history

How to run command in bash without saving it in history?
36
votes
3answers
37k views

SSL Certificate Location on UNIX/Linux

Is there any standard or convention for where SSL certificates and associated private keys should go on the UNIX/Linux filesystem? Thanks.
35
votes
4answers
74k views

how do you create an ssh key for another user?

I'm trying to create an ssh key for another user. I'm logged in as root. Can I just edit the files generated by ssh-keygen and change root to the user I want?
35
votes
15answers
18k 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 ...
35
votes
4answers
20k views

Bind to ports less than 1024 without root access

I would like to run applications I'm working on that binds to port numbers less than 1000 without requiring root access. I'm using Linux Mint and have root access to set it up. I would ideally like ...
35
votes
6answers
48k views

shutdown: What is difference between “Power Off” and “Halt”?

With your typical Linux shutdown command, what is the difference between halting the system and powering off the system?
35
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7answers
37k views

Amazon Linux vs. Ubuntu for Amazon EC2 [closed]

I'm setting up my first website on Amazon EC2, and I'm trying to decide which distro to use. I've used Redhat and CentOS in the past, but I have no bias towards any system, I just want to use whatever ...
35
votes
5answers
26k views

gpg not enough entropy!

SO I've got a ton of processes running in the background to try and get enough entropy but I am still failing. **We need to generate a lot of random bytes. It is a good idea to perform some other ...
35
votes
4answers
19k views

How to make a global ~/.vimrc?

Right now, I make everyone do ~/.vimrc and put their settings there. How can I make a global, default .vimrc for new users?
35
votes
1answer
8k views

Why does `tar -xvfz` fail, but `tar xvfz` work?

tar -xvfz foo.tar.gz returns an error tar: z: Cannot open: No such file or directory This is completely understandable - the f switch expects a filename, and so needs to be last. However, omitting ...
35
votes
2answers
20k views

Damaged /vmlinuz and /initrd.img symbolic links after Kernel uninstall

OS: Ubuntu 8.04 LTS Server Edition We just rolled back an kernel update using the following command: sudo apt-get remove linux-image-2.6.24-24-server The uninstallation was successful, but it had ...
35
votes
5answers
49k views

How do I redirect subdomains to a different port on the same server?

I have some subdomains I want to redirect to specific ports on the same server. Say I have dev.mydomain.com I want dev.mydomain.com to transparently redirect to mydomain.com:8080 and I want to ...
35
votes
5answers
20k views

Job scheduling using crontab, what will happen when computer is shutdown during that time?

I schedule some tasks using crontab. What will happen if my computer is shutdown or turned off during the time when cron was scheduled to do something? Does each missed cron job run after computer ...
34
votes
7answers
67k views

How to get e-mail from (failed) cron-jobs in Ubuntu?

I create cron-jobs in Ubuntu by placing the executable in one of /etc/cron.{daily,hourly,monthly,weekly}. There are lots of directories starting with cron: kent@rat:~$ ls -ld /etc/cron* drwxr-xr-x 2 ...
34
votes
9answers
7k views

Multiple Linux sysadmins working as root

In our team we have three seasoned Linux sysadmins having to administer a few dozen Debian servers. Previously we have all worked as root using SSH public key authentication. But we had a discussion ...
34
votes
10answers
14k views

Securing a fresh Ubuntu server [closed]

Say I've got a fresh install of Ubuntu, what steps should I take to secure it for use as a Rails application server?
34
votes
4answers
29k views

How to disconnect from lxc-console

I'm working with lxc in Ubuntu 12.04, and it's really great. However, I am unable to disconnect from a lxc-console session after I've connected. I read somewhere that Ctrl-aq will disconnect me from ...
34
votes
5answers
55k views

How passively monitor for tcp packet loss? (Linux)

How can I passively monitor the packet loss on TCP connections to/from my machine? Basically, I'd like a tool that sits in the background and watches TCP ack/nak/re-transmits to generate a report on ...
34
votes
3answers
27k views

What's best practice for communication between Amazon EC2 instances?

I've been setting up Amazon EC2 instances for an upcoming project. They are all micro instances, running Ubuntu Server 64bit. Here's what I've setup so far: Web Server -- Apache Database Server --...
33
votes
3answers
22k views

Turn off the Linux OOM killer by default?

The OOM killer on Linux wreaks havoc with various applications every so often, and it appears that not much is really done on the kernel development side to improve this. Would it not be better, as a ...
33
votes
5answers
4k 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 ...
33
votes
4answers
36k views

How to sort ps output by process start time?

Is there a way to sort ps output by process start time, so newest are either at the top or bottom ? On Linux ? On SysV5 ? On Mac ?
33
votes
3answers
73k views

How can I allow one user to su to another without allowing root access?

I'd like to allow certain users to su to another user account without having to know that account's password, but not allow access to any other user account (i.e. root). For instance, I'd like to ...
33
votes
5answers
247k views

How to correct Postfix' 'Relay Access Denied'?

This morning, in order to correct a problem with a name mismatch in the security certificate, I followed the recommended steps from How to fix mail server SSL?, but now, when attempting to send an ...
33
votes
1answer
2k views

Why does removing an unused IP address from an interface kill connections unrelated to that address

Yesterday I did a quick reinstall of a (physical) server in the datacenter, and since I was short on time and with no easy access to our database I just assigned it an IP that I knew was available and ...
33
votes
2answers
3k views

Why was I able to delete a file owned by root in my home directory without being root?

So I was doing some maintenance on my server earlier today and noticed I was able to delete a file owned by root in my home directory. I was able to reproduce a sample: [cbennett@nova ~/temp]$ ls -...
33
votes
6answers
30k views

swap partition vs file for performance?

What is better for performance? A partition closer to the inside of the disk will have slower access times, and we must wait for the drive to switch between the OS and swap partitions. On the other ...
33
votes
7answers
19k views

filesystem for millions of small files

Which Linux filesystem would you choose for best speed in the following scenario: a hundred million files ~2k file size in average >95% read access pretty random access high concurrency (>100 ...
32
votes
9answers
16k views

How to hide a password passed as command line argument?

I'm running a software daemon that requires for certain actions to enter a passphrase to unlock some features which looks for example like that: $ darkcoind masternode start <mypassphrase> ...
32
votes
3answers
25k views

How to get TX/RX bytes without ifconfig?

Since ifconfig is apparently being deprecated in major Linux distributions, I thought I'd learn something about the ip tool that's supposed to be used instead of ifconfig. And here I ran into a ...