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1500 questions
250
votes
12 answers
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 hold a 300DPI image of that size in memory, which…
Ben Dilts
- 2,603
- 3
- 14
- 5
250
votes
11 answers
Terminal prompt not wrapping correctly
I have an issue where if I type in very long commands in bash the terminal will not render what I'm typing correctly. I'd expect that if I had a command like the following:
username@someserver ~/somepath $ ssh -i…
Muricula
- 2,610
249
votes
6 answers
How to extract specific file(s) from tar.gz
How can we extract specific files from a large tar.gz file? I found the process of extracting files from a tar in this question but, when I tried the mentioned command there, I got the error:
$ tar --extract --file={test.tar.gz} {extract11}
tar:…
Ankit Vashistha
- 3,745
249
votes
5 answers
What does env x='() { :;}; command' bash do and why is it insecure?
There is apparently a vulnerability (CVE-2014-6271) in bash: Bash specially crafted environment variables code injection attack
I am trying to figure out what is happening, but I'm not entirely sure I understand it. How can the echo be executed as…
jippie
- 14,086
248
votes
4 answers
Combined `mkdir` and `cd`?
is there any way (what is the easiest way in bash) to combine the following:
mkdir foo
cd foo
The manpage for mkdir does not describe anything like that, maybe there is a fancy version of mkdir? I know that cd has to be shell builtin, so the same…
Jasper
- 3,628
247
votes
9 answers
What does etc stand for?
What does the "etc" folder in the root directory stand for? I think knowing this will help me remember where certain files are located.
Update: Might be useful for others, the folder is used for "Host specific configuration files" - reference.
David Tang
- 2,581
247
votes
11 answers
How can I edit multiple files in Vim?
I know I can open multiple files with vim by doing something like vim 2011-12*.log, but how can I switch between files and close the files one at a time?
Also, how can I tell the file name of the current file that I'm editing?
cwd
- 45,389
246
votes
4 answers
How to export a GPG private key and public key to a file
I have generated keys using GPG, by executing the following command
gpg --gen-key
Now I need to export the key pair to a file;
i.e., private and public keys to private.pgp and public.pgp, respectively.
How do I do it?
rocky
- 2,563
246
votes
3 answers
Why is 'ls' suddenly wrapping items with spaces in single quotes?
I just noticed that on one of my machines (running Debian Sid) whenever I type ls any file name with spaces has single quotes surrounding it.
I immediately checked my aliases, only to find them intact.
wyatt@debian630:~/testdir$ ls
'test 1.txt' …
Wyatt Ward
- 4,032
245
votes
2 answers
There are stopped jobs (on bash exit)
I get the message There are stopped jobs. when I try to exit a bash shell sometimes. Here is a reproducible scenario in python 2.x:
ctrl+c is handled by the interpreter as an exception.
ctrl+z 'stops' the process.
ctrl+d exits python for…
ThorSummoner
- 4,422
245
votes
8 answers
What's the difference between /sbin/nologin and /bin/false
Technically, unless pam is set up to check your shell with pam_shells neither of these can actually prevent your login, if you're not on the shell. On my system they are even different sizes, so I suspect they actually do something. So what's the…
xenoterracide
- 59,188
- 74
- 187
- 252
244
votes
4 answers
How can get a list of all scheduled cron jobs on my machine?
My sysadmin has set up a bunch of cron jobs on my machine. I'd like to know exactly what is scheduled for what time. How can I get that list?
Frank
- 2,781
244
votes
15 answers
How to run a specific program as root without a password prompt?
I need to run something as sudo without a password, so I used visudo and added this to my sudoers file:
MYUSERNAME ALL = NOPASSWD: /path/to/my/program
Then I tried it out:
$ sudo /path/to/my/program
[sudo] password for MYUSERNAME:
Why does it ask…
LanceBaynes
- 40,135
- 97
- 255
- 351
244
votes
3 answers
What's the difference between semicolon and double ampersand &&
What is the difference between
echo "Hello " ; echo "world"
and
echo "Hello " && echo "world"
Both seems to run the two commands after each other.
lindhe
- 4,236
- 3
- 21
- 35
244
votes
9 answers
Find where inodes are being used
So I received a warning from our monitoring system on one of our boxes that the number of free inodes on a filesystem was getting low.
df -i output shows this:
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/xvda1 524288 422613 …
phemmer
- 71,831