These questions are about Linux in general -- NOT specific to a particular distribution. If the question just happens to be in a Linux environment, please specify your Linux distribution in the body of your question, but do NOT use the /linux tag.

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25
votes
1answer
38k 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.
25
votes
4answers
17k views

What is the difference between the following kernel Makefile terms: vmlinux, vmlinuz, vmlinux.bin, zimage & bzimage?

While browsing through the Kernel Makefiles, i found these terms. So i would like to know what is the difference between vmlinux, vmlinuz, vmlinux.bin, zimage & bzimage?
25
votes
3answers
3k views

How can I set the processor affinity of a process on Linux?

The question is all in the title: How can I set the processor affinity of a process on Linux?
25
votes
2answers
94k 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 ...
24
votes
6answers
50k views

Linux ls to show only filename date and size

How can I use ls in linux to get a listing of filenames date and size only. I don't need to see the other info such as owner or permission. Is this possible?
24
votes
5answers
6k views

Is CTRL+C incorrect to use to return to command line?

When I'm using tail -f and I want to return to the shell, I always use CTRL+C. Or when I am typing a command and feel like aborting it and starting over, I simply CTRL+C to get back to an empty ...
24
votes
6answers
37k views

How to replace one char with another in all filenames of the current directories?

How do you rename all files/subdirs in the current folder? Lets say, I have many files and subdirs that are with spaces and I want to replace all the spaces with an underscore. File 1 File 2 File 3 ...
24
votes
3answers
39k views

Linux network troubleshooting and debugging

From time to time Linux and Unix users faced with various network problems. Many of these problems are presented here and at some others troubleshooting forums, but the are very concrete and contains ...
24
votes
3answers
14k views

Understanding /dev and its subdirs and files

$ ls -l /dev/stdin /dev/fd/0 lrwx------ 1 tim tim 64 2011-08-07 09:53 /dev/fd/0 -> /dev/pts/2 lrwxrwxrwx 1 root root 15 2011-08-06 08:14 /dev/stdin -> /proc/self/fd/0 $ ls -l /dev/pts/2 /proc/...
24
votes
7answers
5k views

How to achieve portability with sed -i (in-place editing)?

I'm writing shell scripts for my server, which is a shared hosting running FreeBSD. I also want to be able to test them locally, on my PC running Linux. Hence, I'm trying to write them in a portable ...
24
votes
3answers
44k views

Yum: How can I view variables like $releasever, $basearch & $YUM0?

I am setting up a yum repository, and need to debug some of the URLs in the yum.conf file. I need to know why is Scientific Linux trying to grab this URL, when I was expecting it to grab another URL: ...
24
votes
4answers
28k views

sending text input to a detached screen

I'm trying to run a minecraft server on my unRAID server. The server will run in the shell, and then sit there waiting for input. To stop it, I need to type 'stop' and press enter, and then it'll ...
24
votes
6answers
45k views

How to see disk details like manufacturer in Linux

With sfdisk -s I can see the disk capacity as follows: $ sfdisk -s /dev/cciss/c0d0: 143338560 total: 143338560 blocks How do I see disk details like disk manufacturer? I tried hdparm, but got an ...
24
votes
2answers
19k views

How to update linux “locate” cache

How can i update the cache / index of locate? I installed new packages and the files are clearly not yet indexed. So which command do I have to ommit, in order for the indexer to trigger. I'm ...
24
votes
5answers
83k views

Using the not equal operator for string comparison

if [ "$PHONE_TYPE" != "NORTEL" ] || [ "$PHONE_TYPE" != "NEC" ] || [ "$PHONE_TYPE" != "CISCO" ] then echo "Phone type must be nortel,cisco or nec" exit fi The above code did not work for me, so I ...
24
votes
2answers
10k views

When was a process started

To know when was a process started, my first guess was to check the time when /proc/<pid>/cmdline was written/modified the last time. ps also shows a START field. I thought both of these ...
24
votes
4answers
8k views

Linux: Kill process based on arguments

How can I kill a process based on its command line arguments? killall, pgrep, and pkill seem to only work based on the process name. I need this to be able to differentiate between a number of ...
24
votes
6answers
289k views

How to mount a device in Linux?

I read some resources about the mount command for mounting devices on Linux, but none of them is clear enough (at least for me). On the whole this what most guides state: $ mount (lists all ...
24
votes
1answer
72k views

How do I get sar to show for the previous day?

on our servers, typing sar show's the system load statistics for today starting at midnight, is it possible to show yesterdays statistics?
24
votes
3answers
945 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 ...
24
votes
2answers
35k 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 ...
24
votes
1answer
6k 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.
24
votes
6answers
8k 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 best/...
23
votes
3answers
2k views

How can I shutdown a RHEL server at 06:45 tomorrow morning?

I just received notification that our site has a power outage tomorrow morning. I am a Windows admin but I have to cover for our Linux admin who's not around until tomorrow evening. I need to ...
23
votes
3answers
27k views

How to know where a program is stuck in linux?

I am running the following command on my ubuntu server root@slot13:~# lxc-stop --name pavan --logfile=test1.txt --logpriority=trace It seems to hang indefinitely. Whenever this happened on AIX, I ...
23
votes
8answers
5k 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?
23
votes
6answers
26k views

Execute a specific command in a given directory without cd'ing to it?

Is there a way to execute a command in a different directory without having to cd to it? I know that I could simply cd in and cd out, but I'm just interested in the possibilities of forgoing the extra ...
23
votes
6answers
74k views

How can I look up a username by id in linux?

The command id can be used to look up a user's uid, for example: $ id -u ubuntu 1000 Is there a command to lookup up a username from a uid? I realize this can be done by looking at the /etc/passwd ...
23
votes
4answers
13k views

What doesn't need defragmentation? Linux or the ext2 ext3 FS?

Why don't you have to defrag a Linux system? Because it's using the ext2/ext3 file system or because it's Linux? That's relevant, because a have a double boot system (W7 / Ubuntu) and a common ...
23
votes
7answers
17k views

Is there any (good) SQLite GUI for Linux?

I'm looking for a SQLite graphical administration utility for Linux but I can't seem to find any (I found an extension for Firefox I'm not a user of that browser). Is there any that you know of?
23
votes
3answers
2k views

When is a reboot required?

Apart from upgrading the kernel, are there any changes to a Linux system that require a reboot? I know there are situations where a reboot makes things easier, but are there any that cannot be ...
23
votes
3answers
36k views

what is the meaning of 0.0.0.0 as a gateway?

Can anyone clarify gateway assignment for me? What is the difference between adding gateway as 0.0.0.0 and assigning a specific ip address as a gateway?
23
votes
4answers
19k views

How to check that AES-NI is supported by my CPU?

Howcan I check if my CPU supports the AES-NI instruction set under Linux/UNIX.
23
votes
3answers
29k 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 ...
23
votes
3answers
16k views

Determining Specific File Responsible for High I/O

This is a simple problem but the first time I've ever had to actually fix it: finding which specific files/inodes are the targets of the most I/O. I'd like to be able to get a general system overview, ...
23
votes
1answer
995 views

How does Linux determine what facilities to use to run a (non-text) binary?

I understand that Linux uses shebang line to determine what interpreter to use for scripting languages, but how does it work for binaries? I mean I can run Linux binaries, and having installed both ...
23
votes
3answers
20k views

How to run a script with systemd right before shutdown?

What do I need to put in the [install] section, so that systemd runs /home/me/so.pl right before shutdown and also before /proc/self/net/dev gets destroyed? [Unit] Description=Log Traffic [Service] ...
23
votes
7answers
9k views

How can I use DD to migrate data from an old drive to a new drive?

I am upgrading the internal SATA hard drive on my laptop from a 40G drive to a 160G drive. I have a Linux/Ubuntu desktop which has a SATA card. I would actually like to do the same thing for a couple ...
23
votes
5answers
2k views

How to strip a Linux system?

I've been building a Linux distro, and I've stripped the binaries, etc. The system won't use GCC or development tools, as it will be a Chrome kiosk, so it would greatly help if I could strip down the ...
22
votes
4answers
35k 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?
22
votes
2answers
4k views

Where is the fork() on the fork bomb :(){ :|: & };:?

Warning: Running this command in most shells will result in a broken system that will need a forced shutdown to fix I understand the recursive function :(){ :|: & };: and what it does. But I don'...
22
votes
6answers
8k views

How to safely turn off swap permanently? (on Debian Jessie)

I fresh installed Debian Jessie with default partitioning on an SSD drive. My current disk partitions look like this: As I have 16GB RAM, I think I don't need swap. On Windows, I had it turned off ...
22
votes
3answers
36k 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 ...
22
votes
6answers
28k views

How to find which process is regularly writing to disk?

How can I find which process is constantly writing to disk? I like my workstation to be close to silent and I just build a new system (P8B75-M + Core i5 3450s -- the 's' because it has a lower max ...
22
votes
6answers
9k views

Can ps display only non kernel processes on Linux?

How can I ask ps to display only user processes and not kernel threads? See this question to see what I mean...
22
votes
2answers
85k views

Remove GPT - Default back to MBR

I keep receiving this error: Warning!! Unsupported GPT (GUID Partition Table) detected. Use GNU Parted I want to go back to the normal MBR. I found some advice here and did: parted /dev/sda ...
22
votes
2answers
9k 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 ...
22
votes
3answers
7k 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 tty=...
22
votes
2answers
7k views

How does one change the delay that occurs after entering an incorrect password?

After entering an incorrect password at a login prompt, there s an approximately 3-second delay. How can I change that on a Linux system with PAM?
22
votes
4answers
3k views

Kernel Hacking Environment

I have been working in embedded OS like uCOS, ThreadX. While I have coded apps in Linux, now I’m planning to start learning Linux Kernel. I have few questions regarding the environment. Which is ...