Questions tagged [linux]

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

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1419 votes
39 answers

How can I sort du -h output by size

I need to get a list of human readable du output. However, du does not have a "sort by size" option, and piping to sort doesn't work with the human readable flag. For example, running: du | sort -...
Tom Feiner's user avatar
  • 17.6k
782 votes
9 answers

Can scp copy directories recursively?

Currently I can only copy a single .tar file. But how can I copy directories recursively with scp?
kernel's user avatar
  • 8,571
582 votes
3 answers

What exactly do the colors in htop status bars mean?

By default, htop shows colored status bars for processors, memory, and swap. From left to right, the bars are colored green, blue, yellow, and red depending on some thresholds. What does it mean when ...
tobym's user avatar
  • 6,271
401 votes
20 answers

How to run a server on port 80 as a normal user on Linux?

I have Googled about a solution for quite some time, but couldn't find an answer. I am on Ubuntu Linux and want to run a server on port 80, but due to security mechanism of Ubuntu, I get the ...
Deepak Mittal's user avatar
382 votes
7 answers

Why is my crontab not working, and how can I troubleshoot it?

This is a Canonical Question about using cron & crontab. You have been directed here because the community is fairly sure that the answer to your question can be found below. If your question is ...
Eric Leschinski's user avatar
376 votes
20 answers

Showing total progress in rsync: is it possible?

I have searched for this option already, but have only found solutions that involve custom patching. The fact that it does not show in --help and no more info can be found probably indicates the ...
Aron Rotteveel's user avatar
371 votes
6 answers

What permissions should my website files/folders have on a Linux webserver?

This is a Canonical Question about File Permissions on a Linux web server. I have a Linux web server running Apache2 that hosts several websites. Each website has its own folder in /var/www/. /var/...
Nic's user avatar
  • 13.4k
362 votes
5 answers

Anyone else experiencing high rates of Linux server crashes during a leap second day?

*NOTE: if your server still has issues due to confused kernels, and you can't reboot - the simplest solution proposed with gnu date installed on your system is: date -s now. This will reset the ...
Bron Gondwana's user avatar
340 votes
4 answers

What are the functional differences between .profile .bash_profile and .bashrc

What are the functional differences between the .profile, .bash_profile and .bashrc files?
lollercoaster's user avatar
337 votes
18 answers

Copying a large directory tree locally? cp or rsync?

I have to copy a large directory tree, about 1.8 TB. It's all local. Out of habit I'd use rsync, however I wonder if there's much point, and if I should rather use cp. I'm worried about permissions ...
Amandasaurus's user avatar
  • 31.5k
336 votes
27 answers

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 ...
gareth_bowles's user avatar
312 votes
8 answers

How to bind MySQL server to more than one IP address?

Is there a secret way to bind MySQL to more than one IP address? As far as I can see the bind-address parameter in the my.cnf does not support more than one IP and you can't have it more than once.
BlaM's user avatar
  • 3,906
294 votes
8 answers

Check if port is open or closed on a Linux server?

How can I check if a port is listening on a Linux server?
James Anderson's user avatar
283 votes
13 answers

Can I nohup/screen an already-started process?

I'm doing some test-runs of long-running data migration scripts, over SSH. Let's say I start running a script around 4 PM; now, 6 PM rolls around, and I'm cursing myself for not doing this all in ...
ojrac's user avatar
  • 2,933
275 votes
3 answers

Moving an already-running process to Screen

My office job routinely sees me connected to a Linux box via VNC. Sometimes I start a remote job on the console, and realize later that it runs much longer than expected. (Should have started that ...
DevSolar's user avatar
  • 2,926
271 votes
2 answers

Why is "chmod -R 777 /" destructive?

This is a Canonical Question about File Permission and Why 777 is "destructive". I'm not asking how to fix this problem, as there are a ton of references of that already on Server Fault (reinstall OS)...
samwise's user avatar
  • 2,413
266 votes
2 answers

Linux command to inspect TXT records of a domain [closed]

Is there a linux shell command that I can use to inspect the TXT records of a domain?
John's user avatar
  • 7,363
266 votes
5 answers

Why does my hostname appear with the address rather than in /etc/hosts?

This may be a bit of a noobish question, but I was taking a look at /etc/hosts on my new Xubuntu install and saw this: localhost myhostname On most 'nixes I've used, the second ...
Tom's user avatar
  • 3,213
262 votes
11 answers

How can I run Debian stable but install some packages from testing?

Say you're running a server and you don't want to upgrade to Testing (Squeeze) from Stable (Lenny) to just install a required package or two. What's the best way of installing only certain packages ...
Gareth's user avatar
  • 8,573
252 votes
10 answers

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 ...
warren's user avatar
  • 18.4k
245 votes
13 answers

Environment variables of a running process on Unix?

I need to troubleshoot some problems related to environment variables on a Unix system. On Windows, I can use a tool such as ProcessExplorer to select particular a process and view values of each ...
Gant's user avatar
  • 2,595
241 votes
10 answers

How to run a command multiple times, using bash shell?

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. Update: The reason I am asking this is,...
mahatmanich's user avatar
  • 2,954
238 votes
16 answers

df in linux not showing correct free space after file removal

I have file servers which are used to store files. Files might reside there for a week, or for a year. Unfortunately, when I remove files from the server, df command doesn't reflect the freed up space....
user avatar
234 votes
4 answers

What's the best way of handling permissions for Apache 2's user www-data in /var/www?

Has anyone got a nice solution for handling files in /var/www? We're running Name Based Virtual Hosts and the Apache 2 user is www-data. We've got two regular users & root. So when messing with ...
Gareth's user avatar
  • 8,573
231 votes
19 answers

In my /etc/hosts/ file on Linux/OSX, how do I do a wildcard subdomain?

I need to test sub-domains on my localhost. How can I effectively have this result of adding * to my /etc/hosts/ file? If it's not possible, how do I work around this problem? I need ...
MikeN's user avatar
  • 8,462
228 votes
17 answers

Permission denied (publickey). SSH from local Ubuntu to Amazon EC2 server

I have an instance of an application running in the cloud on an Amazon EC2 instance, and I need to connect to it from my local Ubuntu. It works fine on one local ubuntu and also laptop. I got this ...
Vorleak Chy's user avatar
  • 2,421
227 votes
3 answers

How do I do 'mount --bind' in /etc/fstab?

I'm trying to add mount --bind /proc/ /chroot/mysql/proc to /etc/fstab. How can I do this?
Some Linux Nerd's user avatar
226 votes
10 answers

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.
hasen's user avatar
  • 2,544
226 votes
8 answers

When does /tmp get cleared?

I'm taking to putting various files in /tmp, and I wondered about the rules on deleting them? I'm imagining it's different for different distributions, and I'm particularly interested in Ubuntu and ...
John Lawrence Aspden's user avatar
222 votes
14 answers

Shell command to monitor changes in a file

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 ...
Sebastian Hoitz's user avatar
217 votes
8 answers

Setting the hostname: FQDN or short name?

I've noticed that the "preferred" method of setting the system hostname is fundamentally different between Red Hat/CentOS and Debian/Ubuntu systems. CentOS documentation and the RHEL deployment guide ...
Cakemox's user avatar
  • 25.2k
208 votes
8 answers

How to setup passwordless `sudo` on Linux?

How can passwordless sudo access be setup on either RHEL (Fedora, CentOS, etc) or Ubuntu distributions? (If it's the same across distros, that's even better!) Setting: personal and/or lab/training ...
warren's user avatar
  • 18.4k
206 votes
15 answers

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 ...
palehorse's user avatar
  • 4,319
206 votes
5 answers

Difference in sites-available vs sites-enabled vs conf.d directories (Nginx)?

I have some experience using linux but none using nginx. I have been tasked with researching load-balancing options for an application server. I have used apt-get to install nginx and all seems ...
Seth Spearman's user avatar
202 votes
4 answers

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 Swap:...
Muahmmad Zeeshan's user avatar
196 votes
6 answers

How to cd into a directory with this name "-2" (starting with the hyphen)?

I have a directory named: -2 I want to cd into it but the cd complains: bash: cd: -2: invalid option With no success, I've tried: cd "-2" cd '-2' cd \-2 Any solution? Edit: no file browsers ...
user151851's user avatar
  • 1,863
196 votes
22 answers

Is it normal to get hundreds of break-in attempts per day?

I just checked my server's /var/log/auth.log and found that I'm getting over 500 failed password/break-in attempt notifications per day! My site is small, and its URL is obscure. Is this normal? ...
Kyle Cureau's user avatar
  • 1,537
195 votes
6 answers

LVM dangers and caveats

I have recently started using LVM on some servers for hard drives larger than 1 TB. They're useful, expandable and quite easy to install. However, I could not find any data about the dangers and ...
Adam Matan's user avatar
  • 13.3k
193 votes
6 answers

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. edit:...
Stepan's user avatar
  • 2,149
193 votes
3 answers

What does a + mean at the end of the permissions from ls -l?

What is the plus sign at the end of the permissions telling me? ls -l total 4 drwxrwxrwx+ 2 benson avahi-autoipd 4096 Jan 27 17:37 docs Here's the context: cat /etc/issue \CentOS release 5.3 (Final)...
bmargulies's user avatar
  • 2,333
192 votes
15 answers

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

After I have installed a package by yum (with multiple repositories configured), how can I find from which repository it has been installed? If I run yum info package-name (or yum list package-name), ...
lg.'s user avatar
  • 4,649
190 votes
4 answers

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 ...
Zhen's user avatar
  • 2,159
189 votes
6 answers

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?
John Topley's user avatar
  • 2,195
187 votes
10 answers

How do I verify the speed of my NIC?

I just installed a new gigabit network interface card (NIC) in Linux. How do I tell if it is really set to gigabit speeds? I see ethtool has an option to set the speed, but I can't seem to figure ...
User1's user avatar
  • 2,506
183 votes
10 answers

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-...
Maxim Veksler's user avatar
182 votes
31 answers

How do I prevent accidental rm -rf /*?

I just ran rm -rf /* accidentally, but I meant rm -rf ./* (notice the star after the slash). alias rm='rm -i' and --preserve-root by default didn't save me, so are there any automatic safeguards for ...
Valentin Nemcev's user avatar
179 votes
8 answers

Filename length limits on linux?

Are there any filename or path length limits on Linux?
readonly's user avatar
  • 3,369
178 votes
8 answers

How do I sleep for a millisecond in bash or ksh

sleep is a very popular command and we can start sleep from 1 second: # wait one second please sleep 1 but what the alternative if I need to wait only 0.1 second or between 0.1 to 1 second ? ...
yael's user avatar
  • 2,433
175 votes
18 answers

Disk full, du tells different. How to further investigate?

I have a SCSI disk in a server (hardware Raid 1), 32G, ext3 filesytem. df tells me that the disk is 100% full. If I delete 1G this is correctly shown. However, if I run a du -h -x / then du tells me ...
initall's user avatar
  • 2,325
175 votes
9 answers

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 realize ...
mike's user avatar
  • 3,963

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