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1500 questions
104
votes
11 answers

How do I echo just 1 column of output from ls command?

Lets say when I do ls command the output is: file1 file2 file3 file4 Is it possible to display only a certain column of output, in this case file2? I have tried the following with no success: echo ls | $2 Basically all I want to do is echo only…
John
  • 3,599
103
votes
2 answers

Make xargs pass as first parameter

I'm trying to produce this behaviour: grep 192.168.1 *.txt By passing a string into grep via Xargs but it is going on the end instead of as the first parameter. echo 192.168.1 | xargs grep *.txt I need to tell xargs (or something similar) to put…
andy boot
  • 1,193
103
votes
8 answers

Creating a ram disk on Linux

I have a machine with 62GB of RAM, and a trunk that's only 7GB, so I thought I would create a RAM disk and compile there. I am not a Linux expert. I found instructions on the internet to create the RAM disk: mkfs -q /dev/ram1 8192 but I changed…
Frank
  • 1,031
103
votes
5 answers

What is the point of sshd “UseDNS” option?

I know what it does, but I don't know why. What attack(s) does it prevent? Is it relevant for all kind of authentication methods? (hostbased, password, publickey, keyboard-interactive ...)
user368507
  • 2,173
103
votes
2 answers

How do I copy a symbolic link?

I have a symbolic link to a file in one directory. I would like to have that same link in another directory. How do I copy a symbolic link? I tried to cp the symbolic link but this copies the file it points to instead of the symbolic link itself.
User
  • 2,297
103
votes
4 answers

Replacing only specific variables with envsubst

I'm trying to perform environment variable replacement through envsubst, but I want to only replace specific variables. From the docs I should be able to tell envsubst to only replace certain variables but I'm failing to be able to do that. For…
João Angelo
  • 1,133
103
votes
8 answers

How do you list number of lines of every file in a directory in human readable format.

I have a list of directories and subdirectories that contain large csv files. There are about 500 million lines in these files, each is a record. I would like to know How many lines are in each file. How many lines are in directory. How many…
Hexatonic
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103
votes
3 answers

Rebuild auto-complete index (or whatever it's called) and binaries in $PATH cache in zsh

After installing new software, an already opened terminal with zsh won't know about the new commands and cannot generate auto-complete for those. Apparently opening a new terminal fix the problem, but can the index (or whatever you call it) be…
phunehehe
  • 20,240
103
votes
4 answers

Command to list PostgreSQL user accounts?

There are createuser & dropuser commands: createuser - define a new PostgreSQL user account dropuser - remove a PostgreSQL user account Is there a corresponding way to list the user accounts? These two commands do not require the user to invoke…
CW Holeman II
  • 3,684
103
votes
5 answers

How to find out if a system uses SysV, Upstart or Systemd initsystem

Is there a simple way to find out which initsystem is being used e.g by a recent Debian wheezy or Fedora system? I'm aware that Fedora 21 uses systemd initsystem but that is because I read that and because all relevant scripts/symlinks are stored…
Valentin Bajrami
  • 9,344
103
votes
2 answers

Difference between 'echo' and 'echo -e'

What is the difference between echo and echo -e? And which quotes ("" or '') should be used with the echo command? i.e: echo "Print statement" or echo 'Print statement'? Also, what are the available options that can be used along with echo?
Venkatesh
  • 1,171
103
votes
8 answers

Does /usr/sbin/nologin as a login shell serve a security purpose?

In my /etc/passwd file, I can see that the www-data user used by Apache, as well as all sorts of system users, have either /usr/sbin/nologin or /bin/false as their login shell. For example, here is a selection of…
Mark Amery
  • 3,000
103
votes
5 answers

Recover cron jobs accidently removed with crontab -r

I entered crontab -r instead of crontab -e and all my cron jobs have been removed. What is the best way (or is there one) to recover those jobs?
Teerath Kumar
  • 1,135
102
votes
5 answers

Remove line containing certain string and the following line

I use this cat foo.txt | sed '/bar/d' to remove lines containing the string bar in the file. I would like however to remove those lines and the line directly after it. Preferably in sed, awk or other tool that's available in MinGW32. It's a kind of…
jakub.g
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102
votes
1 answer

Make cd follow symbolic links

I have my code mounted as an sshfs in my home directory, but the hierarchy is difficult to remember, so I created a symlink in my home directory leading to that directory. Is there a way so that when I cd to that symbolic link, instead of cding to…
rowantran
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