Questions specifically about Linux but not specific to a particular distribution. If the question could apply to any Unix-like system, specify your Linux distribution in the body of your question but do not use the /linux tag.

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21
votes
2answers
4k views

How do I make a file NOT modifiable?

While logged in, I can do the following: mkdir foo touch foo/bar chmod 400 foo/bar chmod 500 foo Then I can open vim (not as root), edit bar, force a write with w!, and the file is modified! How ...
21
votes
2answers
6k views

How do I remove a file with no permissions?

A hacker has dropped a file in my tmp dir that is causing issues. Nothing malicious except creating GB's of error_log entries because their script is failing. However, the file they are using to ...
21
votes
2answers
15k views

How to colorize output of ls ?

I'm running CentOS in Linux text mode. When I run the command ls /usr/, the output is too hard to read (dark blue on black). How can I change the text coloring?
21
votes
4answers
865 views

Making Linux read swap back into memory

The Linux kernel swaps out most pages from memory when I run an application that uses most of the 16GB of physical memory. After the application finishes every action (typing commands, switching ...
21
votes
7answers
88k views

Unix/Linux undelete/recover deleted files

Is there a command to recover/undelete deleted files by rm? $ rm -rf /path/to/myfile How can I recover myfile? If there is such a tool how can I use it?
21
votes
6answers
6k views

What's the most “correct” mount point for a permanent NTFS partition?

I have an NTFS partition (containing a Windows installation from which I dual boot) that I would like to permanently mount from my Linux installation. Problem is, I can't figure out what the ...
20
votes
4answers
23k views

How do I make multiple directories at once in a directory?

I know with mkdir I can do mkdir A B C D E F to create each directory. How do I create directories A-Z or 1-100 with out typing in each letter or number?
20
votes
5answers
3k views

Understanding UNIX based permissions and their attributes

I've never really got how chmod worked up until today. I followed a tutorial that explained a big deal to me. For example, I've read that you've got three different permission groups: owner (u) ...
20
votes
8answers
4k views

The most universal scripting language for Linux is?

We are writing scripts for Linux systems, there has been some debate over what would be the most universally Linux present scripting language to use. Bash, SH, Posix? What?
20
votes
3answers
7k views

Why does Linux use a swap partition rather than a file?

It seems to me a swap file is more flexible.
20
votes
4answers
1k views

Is there a reason why 'owner' permissions exist? Aren't group permissions enough?

I think I rather understand how file permissions work in linux. However, I don't really understand why they are split into three levels and not into two. I'd like the following issues answered: Is ...
20
votes
5answers
5k views

Where does uname get its information from?

Where does uname really get its information from? I figure this is something that should be straightforward. Unfortunately, I can't find any header containing just that information. Say someone ...
20
votes
2answers
10k views

/proc/PID/fd/X link number

In Linux, in /proc/PID/fd/X, the links for file descriptors that are pipes or sockets have a number, like: l-wx------ 1 user user 64 Mar 24 00:05 1 -> pipe:[6839] l-wx------ 1 user user 64 Mar 24 ...
20
votes
4answers
27k views

How is an Interrupt handled in Linux?

I just know that Interrupt is a hardware signal assertion caused in a processor pin. But I would like to know how Linux OS handles it. What all are the things that happen when an interrupt occurs?
20
votes
1answer
28k views

How is a message queue implemented in the Linux kernel?

I would like to know how Message Queues are implemented in the Linux Kernel.
20
votes
3answers
413 views

How did the Linux Kernel project track bugs in the Early Days?

We all know that Linus Torvalds created Git because of issues with Bitkeeper. What is not known (at least to me) is, how were issues/tickets/bugs tracked up until then? I tried but didn't get anything ...
20
votes
1answer
4k views

Run a command for a specified time and then abort if time exceeds

I want know how I can run a command for a specified time say, one minute and if it doesn't complete execution then I should be able to stop it.
20
votes
2answers
79k views

How to find the installation path for a software under linux?

Under linux, I launch a software by typing, e.g., fluidplot. How can I find the installation path for this software?
20
votes
2answers
59k views

How can I change a user's default group in Linux?

Being new to Linux administration, I'm a little confused about the following commands: useradd usermod groupadd groupmod I've just finished reading the user administration book in the Linux/Unix ...
20
votes
2answers
17k views

how to check rx ring, max_backlog, and max_syn_backlog size

Quite often in the course of troubleshooting and tuning things I find myself thinking about the following Linux kernel settings: net.core.netdev_max_backlog net.ipv4.tcp_max_syn_backlog ...
20
votes
4answers
22k views

How to record Skype video calls on Linux?

I'd like to conduct recorded video interviews with Skype and am looking for a reliable tool to accomplish that. Is there anything out there that's not slow or buggy? I'm running (K)Ubuntu.
19
votes
5answers
18k views

How can I limit the bandwidth used by a process?

I have a CentOS 5.7 server that will be backing up its files nightly. I am concerned that visitors to the various sites that the server hosts will experience degraded performance while the backup is ...
19
votes
3answers
3k views

Standard and/or common directories on Unix/Linux OSes

Coming from the Windows world, I have found the majority of the folder directory names to be quite intuitive: \Program Files contains files used by programs (surprise!) \Program Files (x86) contains ...
19
votes
6answers
16k views

How can I see dmesg output as it changes?

I'm writing a device driver that prints error message into ring buffer dmesg output. I want to see the output of dmesg as it changes. How can I do this?
19
votes
3answers
7k views

When should I use a trailing slash on a directory? [duplicate]

Possible Duplicate: How linux handles multiple path separators (/home////username///file) Most commands I use in linux behave exactly the same whether I include the trailing slash / ...
19
votes
4answers
24k views

What is a spinlock in Linux?

I would like to know about spinlocks in detail? Could someone explain that to me?
19
votes
5answers
38k views

How can I find the hardware model in Linux?

I used a system information utility to take the model number of a system, and also of the motherboard. DMI System Manufacturer LENOVO DMI System Product 2306CTO DMI System Version ...
19
votes
4answers
6k views

Why does dd from /dev/random give different file sizes?

I am running the following command on an ubuntu system: dd if=/dev/random of=rand bs=1K count=2 However, every time I run it, I end up with a file of a different size. Why is this? How can I ...
19
votes
3answers
18k views

What is stored in /dev/pts files and can we open them?

According to my knowledge, /dev/pts files are created for ssh or telnet sessions.
19
votes
2answers
51k views

How to display open file descriptors but not using lsof command

Hi I have read Here that lsof is not an accurate way of getting the number of File Descriptors that are currently open. He recommended to use this command instead cat /proc/sys/fs/file-nr While ...
19
votes
3answers
23k views

What is the most high-performance Linux filesystem for storing a lot of small files (HDD, not SSD)?

I have a directory tree that contains many small files, and a small number of larger files. The average size of a file is about 1 kilobyte. There are 210158 files and directories in the tree (this ...
19
votes
3answers
20k views

Where can I see a list of kernel killed processes?

Is there some way I can check which of my processes the kernel has killed? Sometimes I log onto my server and find that something that should've run all night just stopped 8 hours in and I'm unsure if ...
19
votes
2answers
14k views

Reply on same interface as incoming?

I have a system with two interfaces. Both interfaces are connected to the internet. One of them is set as the default route; a side effect of this is that if a packet comes in on the non-default-route ...
19
votes
3answers
6k views

Why does the 'bin' user need a login shell?

During an audit of /var/log/auth.log on one of my public webservers, I found this: Jan 10 03:38:11 Bucksnort sshd[3571]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 ...
19
votes
2answers
5k views

How does sudo remember you already entered root's password?

When using sudo on Linux, it asks for root password, but only the first time you run it. If you run another sudo command, it remember you already entered the password previously and doesn't ask for ...
19
votes
6answers
2k views

Is there a way to limit overall CPU consumption?

My laptop (an HP with an i3 chip) overheats like crazy every time I run a resource heavy process (like a large compilation, extracting large tarballs or ... playing Flash). I am currently looking ...
19
votes
7answers
12k views

Linux boot loaders supporting full disk encryption?

Are there any Linux boot loaders supporting full disk encryption (a la TrueCrypt). I know there was work towards adding encryption support to GRUB2, but this does not seem to be ready yet. Any other ...
19
votes
3answers
33k views

Can I connect to Windows machine from Linux shell?

I can connect to Linux machines from Windows using PuTTY/SSH. I want to do the other way round - connect to a Windows machine from Linux. Is this possible?
19
votes
4answers
4k views

What happens to the output of a process that has been disowned and lost its terminal?

If I close the virtual terminal, where some process was started, does the output just go straight to /dev/null, or can it pollute memory somehow? Can I anyhow grab the output to continue reading it at ...
19
votes
3answers
1k views

Can I achieve functionality similar to interrupts in Linux userspace?

One of functionalities I miss the most from "small embedded" in Embedded Linux is the interrupts. A signal appears on a specific pin, or other interrupt source is triggered and whatever was done ...
18
votes
6answers
3k views

Why do most linux distros default gnome? [closed]

Why the default desktop environment of most popular linux distros is gnome? KDE seems to me an equally good desktop environment. Is it for licence reason? historic? or else?
18
votes
7answers
64k views

Show top five CPU consuming processes with `ps`

How to show top five CPU consuming processes with ps?
18
votes
4answers
1k views

Why does Linux scale so well to different hardware platforms?

Why does Linux run well on so many different types of machines - desktops, laptops, servers, embedded devices, mobile phones, etc? Is it mainly because the system is open, so any part of it can be ...
18
votes
4answers
58k views

Why the default eth0 interface is down by default on CentOS?

I am already a little bit familiar with Linux distros like Debian or Ubuntu (yeah, very similar) but I wanted to try Red Hat based - CentOS 6.2 . I have installed it on my Windows 7 host in virtualBox ...
18
votes
2answers
10k views

What is the proper sudoers syntax to add a user?

According to the comments in /etc/sudoers (Fedora 13): ## Syntax: ## ## user MACHINE=COMMANDS ## ## The COMMANDS section may have other options added to it. My two related questions: What ...
18
votes
4answers
8k views

Block Particular Command in Linux for Specific user

How to block command, let say mkdir for specific user ? What I did just created read-only function and store in users profile ~/.bashrc /bin/mkdir() { echo "mkdir command not allow for you" ...
18
votes
2answers
30k views

What is the difference between ioctl(), unlocked_ioctl() and compat_ioctl()?

Going through the linux 2.6.36 source code at lxr.linux.no, I could not find the ioctl() method in file_operations. Instead I found two new calls: unlocked_ioctl() and compat_ioctl(). What is the ...
18
votes
7answers
7k views

Linux equivalent to ReadyBoost?

Is there a kernel module or some other patch or something similar to Windows' ReadyBoost? Basically I'm looking for something that allows disk reads to be cached on a Flash drive.
18
votes
5answers
3k views

Corruption-proof SD card filesystem for embedded Linux?

Recently we had a rather unpleasant situation with our customer - Raspberry Pi based "kiosk" used to display remote sensing data (nothing more fancy than a kiosk mode browser displaying a ...
18
votes
1answer
3k views

Change password on a LUKS filesystem without knowing the password

I have a Debian Wheezy server that's been running for a while with an encrypted drive. The password for the encrypted drive (/dev/sda5) was lost when my encrypted password file was corrupted. I'd ...