54
votes
7answers
22k views

How to check if a shell is login/interactive/batch

I think I understand the differences between an interactive, a login and a batch shell. See the following links for more help: What is the difference between a 'Login' and an 'Interactive' bash ...
63
votes
9answers
3k views

Remember a half-typed command while I check something

I often find myself in the following position: I've started typing a long command at the bash prompt, but half-way through I find out I need to check something with another command. This is a problem ...
40
votes
11answers
24k views

Correct locking in shell scripts?

Sometimes you have to make sure that only one instance of a shell script is running at the same time. For example a cron job which is executed via crond that does not provide locking on its own (e.g. ...
29
votes
4answers
3k views

What are the responsibilities of each Pseudo-Terminal (PTY) component (software, master side, slave side)?

I am trying to figure out how a tty works1 (the work-flow and responsibilities of each elements). I have read several interesting articles about it, but there are still some blurry areas. This is ...
73
votes
6answers
29k views

Can I create a user-specific hosts file to complement /etc/hosts?

Is it possible to add a list of hosts that are only specific to a certain user? Perhaps a user-specific hosts file? This mechanism should also complement the entries in the /etc/hosts file.
43
votes
11answers
17k views

Easy way to determine virtualization technology

I have command line access to a Linux machine which may or may not be virtualized. I want to determine what kind of virtualization technology it runs on, if any (VMWare, VirtualBox, KVM, OpenVZ, Xen, ...
71
votes
12answers
38k views

how do you sort du output by size?

How do you sort du -sh /dir/* by size? I read one site that said use | sort -n but that's obviously not right. Here's an example that is wrong. [~]# du -sh /var/* | sort -n 0 /var/mail 1.2M ...
45
votes
6answers
5k views

Can I configure my shell to print STDERR and STDOUT in different colors?

I want to set my terminal up so stderr is printed in a different color than stdout; maybe red. This would make it easier to tell the two apart. Is there a way to configure this in .bashrc? If not, is ...
33
votes
11answers
29k views

How can I reliably get the operating system's name?

Say I am logged into a remote system, how can I know what it's running? On most modern Linuxes (Linuces?), you have the lsb_release command: $ lsb_release -ic Distributor ID: LinuxMint Codename: ...
28
votes
8answers
32k views

Different ways to execute a shell script

There a several ways to execute a script, the ones I know are: /path/to/script # using the path (absolute or relative) . script # using the . (dot) source script # using the `source` command ...
16
votes
3answers
4k views

Reattach to lost X11 session

I'm using X11 forwarding over ssh to run Linux apps on my Windows box, and when the network drops it loses everything that was running. Is there anything similar to screen for X11?
15
votes
1answer
6k views

How can I configure a reverse SSH connection to the connecting computer?

I'm going to be deploying a number of machines in the near future which will be behind routers. It won't be feasible to set up dynamic DNS on each router and port forwarding, so is there a way I can ...
34
votes
6answers
30k views

How to speed my too-slow ssh login?

Running ssh user@hostname takes ~30s. Here's the scenario: this is a VM on the local LAN Windows and Mac machines get instant login am using Debian and I could reproduce with an Ubuntu machine ...
17
votes
3answers
8k 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 ...
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 ...
15
votes
1answer
5k views

Where should a local executable be placed?

I have an executable for the perforce version control client (p4). I can't place it in /opt/local because I don't have root privileges. Is there a standard location where it needs to be placed under ...
24
votes
3answers
26k views

Installing Grub 2 on a USB flash drive

MultiBootISOs is a tool that let you install Grub on a USB flash drive. I really like it because it lets me boot from ISO files and let me put a bunch of ISOs on my USB and choose which one to boot. ...
23
votes
4answers
69k views

SSH login with clear text password as a parameter?

I need to login to a user that I've created on a remote host running Ubuntu. I can't use an ssh key because the ssh login will happen from a bash script ran within a server that I won't have access to ...
17
votes
2answers
1k views

What does `:-` mean in a shell script

I saw this in the end of an awesome shell script but I can't understand the login here because I think it's being short-handed for a longer command. spark ${@:-`cat`} This apears at the end of this ...
12
votes
1answer
2k views

Can one PC be used by two users at the same time via dual-monitor?

Since modern PCs can use two screens at the same time I wonder if it is possible to plug in two keyboards and mouses as well to have the two screens run two (more or less) independent X-sessions at ...
13
votes
2answers
9k views

Debian based system, only one gui program, nothing else

I would like to make a debian system where you can only open one GUI program at boot, no other graphical interface, no minimize, or any X apart from that program, is there a way to do it on debian if ...
9
votes
2answers
7k views

ssh port forward to access my home machine from anywhere

http://serverfault.com/questions/303937/how-to-make-freebsd-box-accessible-from-internet I want to understand this whole process of port forwarding. I read so many things but failing to understand ...
11
votes
7answers
2k views

determine shell in script during runtime

As per my knowledge, to determine the current shell we use echo $0 in the shell. Rather I want my script to check in which shell it is running. So, I tried to print $0 in the script and it returns the ...
33
votes
7answers
5k views

How to determine where an environment variable came from

I have a linux instance that I set up some time ago. When I fire it up and log in as root there are some environment variables that I set up but I can't remember or find where they came from. I've ...
9
votes
1answer
867 views

Why my ethernet interface is called enp0s10 instead of eth0?

Just that, when I run ifconfig -a I only get lo and enp0s10 interfaces, not the classical eth0 What does enp0s10 means? Why is there no eth0?
9
votes
2answers
4k views

Find filesystem of an unmounted partition from a script

I'm writing a custom automated install using AIF (Arch Installation Framework), and I need to find the filesystem on a partition given a partition. So far I have this: grok_partitions () { local ...
7
votes
5answers
12k views

Transposing rows and columns

I have a file with the lines like below. title1:A1 title2:A2 title3:A3 title4:A4 title5:A5 title1:B1 title2:B2 title3:B3 title4:B4 title5:B5 title1:C1 title2:C2 title3:C3 title4:C4 title5:C5 ...
24
votes
2answers
34k views

How can I increase the number of inodes in an ext4 filesystem?

I had a problem (new to me) last week. I have a ext4 (Fedora 15) filesystem. The application that runs on the server suddenly stopped. I couldn't find the problem at first look. df showed 50% ...
5
votes
1answer
2k views

Reading a filesystem from a whole disk image

I ran these commands: VBoxManage clonehd d6b9f0a5-98df-48ca-83c8-91a0809ec349 --format RAW Debian.raw sudo dd if=~/.VirtualBox/HardDisks/Debian.raw of=/dev/sda5 When I try to mount the partition, I ...
6
votes
1answer
598 views

LoggedFS configuration file syntax

What is the syntax of the LoggedFS configuration file? The official documentation only had usage instructions for the loggedfs command and a configuration file example. Ok, it's XML, but what are ...
6
votes
3answers
757 views

Access to original contents of mount point

On my headless NAS I have sdf1 (a flash-card) mounted as / while /home is mounted from lv00 (an LVM volume backed by a software RAID). To be able to access the machine when the RAID fails, I have a ...
4
votes
1answer
10k views

“No such file or directory” on an executable, yet file exists and ldd reports all libraries present

So by any other command the executable file exists, yet when I try to execute it, it claims it is not there. It is not a special character in the name because I renamed it though a "cat". And it ...
4
votes
2answers
1k views

SSH tunnel through middleman server - how to connect in one step (using key pair)?

My question is basically how to turn my existing two steps into one step. I have a working SSH tunnel set up between two computers using a middleman server like this: ...
4
votes
2answers
1k views

undelete files from local fileserver

I have a NAS (mybook world white light) in my living room where all my music and stuff is stored. I've mounted the music folder of the nas in the local music folder of my home directory on my desktop ...
81
votes
3answers
156k views

How do you empty the buffers and cache on a Linux system?

Prior to doing some benchmarking work how would one free up the memory (RAM) that the Linux Kernel is consuming for its buffers and cache?
202
votes
23answers
132k views

Repeat a Unix command every x seconds forever

There's a built-in Unix command repeat whose first argument is the number of times to repeat a command, where the command (with any arguments) is specified by the remaining arguments to repeat. For ...
80
votes
17answers
11k views

Where should I put software I compile myself?

I need to compile some software on my Fedora machine. Where's the best place to put it so not to interfere with the packaged software?
44
votes
11answers
22k views

Recommended reading to better understand Unix/Linux internals [closed]

I've worked on *nix environments for the last four years as a application developer (mostly in C). Please suggest some books/blogs etc. for improving my *nix internals knowledge.
51
votes
6answers
36k views

How to remove duplicate lines inside a text file?

A huge (up to 2 GiB) text file of mine contains about 100 exact duplicates of every line in it (useless in my case, as the file is a CSV-like data table). What I need is to remove all the repetitions ...
101
votes
4answers
22k views

How do I clear Bash's cache of paths to executables?

When I execute a program without specifying the full path to the executable, and Bash must search the directories in $PATH to find the binary, it seems that Bash remembers the path in some sort of ...
53
votes
5answers
65k views

Limit memory usage for a single Linux process

I'm running pdftoppm to convert a user-provided PDF into a 300DPI image. This works great, except if the user provides an PDF with a very large page size. pdftoppm will allocate enough memory to ...
40
votes
6answers
67k views

How to find creation date of file?

I want to find out the creation date of particular file, not modification date or access date. I have tried with ls -ltrh and stat filename.
34
votes
5answers
7k views

Why do hard links exist?

I know what hard links are, but why would I use them? What is the utility of a hard link?
31
votes
7answers
43k views

Correctly determining memory usage in Linux

I'm a bit confused on some of the results I am seeing from "ps" and "free". On my server, this is the result of "free -m" [root@server ~]# free -m total used free shared ...
28
votes
5answers
49k views

Script to monitor folder for new files?

How do I detect new files in a folder with a bash script? I would like to process the files as soon as they are created in the folder. Is this possible to do so or do I have to schedule a script with ...
42
votes
6answers
18k views

Different linux distros sharing the same /home folder?

What is the best way to share the same /home directories between different linux distribution? I mean, I want to have both, say, Fedora and Arch, and I want to find my files at home no matter which ...
21
votes
4answers
9k views

Quoting in ssh $host $FOO and ssh $host “sudo su user -c $FOO” type constructs

I often end up issuing complex commands over ssh; these commands involve piping to awk or perl one-lines, and as a result contain single quotes and $'s. I have neither been able to figure out a hard ...
10
votes
4answers
9k views

How do I handle switches in a shell script?

Are there some built-in tools that will recognize -x and --xxxx as switches, and not arguments, or do you have to go through all the input variables, test for dashes, and then parse the arguments ...
32
votes
4answers
35k views

Understanding the exclamation mark (!) in bash

I used history | less to get the lines of previous commands and from the numbers on the left hand side I found the line I wanted repeated (eg. 22) and did !22 at the command prompt and it ...
31
votes
5answers
11k views

Measuring RAM usage of a program

time is a brilliant command if you want to figure out how much CPU time a given command takes. I am looking for something similar that can measure the max RAM usage of the program and any children. ...

15 30 50 per page