12
votes
2answers
3k views

What’s the difference between a “raw” and a “cooked” device driver?

Does this concept only apply to terminal drivers (which is what most sites cover) or to any driver in general?
12
votes
2answers
2k views

Suppress output unless non-zero exit code

What's the best way to suppress output (stdout and stderr) unless the program exits with a non-zero code? I'm thinking: quiet_success() { file=$(mktemp) if ! ( "$@" > "$file" 2>&1 ); ...
12
votes
2answers
3k views

“ls -lh” reports total size less than sum of individual sizes

Under what circumstances would ls -lh show a total that is less than the sum of the individual files? For example: $ ls -lh /var/lib/nova/instances/_base total 100G -rw-rw-r-- 1 nova nova 4....
12
votes
3answers
15k views

What are the exact differences between awk and cut with grep? [closed]

We know that we can get the second column of the line we want from a file using these two techniques: awk '/WORD/ { print $2 }' filename or grep WORD filename| cut -f 2 -d ' ' My questions are: ...
12
votes
1answer
5k views

How can I monitor CPU usage by user?

I need to monitor CPU usage by users of two servers' (Ubuntu and CentOS). For example: user1 5% user2 10% ... Is there a tool similar to top or htop that can do that?
12
votes
2answers
4k views

FreeBSD: “Too many open files” but should be able to open another 160,000 files

I have a FreeBSD 8 system running ZFS, with a MySQL 5.5 server which is about 355GB and projected to grow to be a couple of Terabytes. MySQL is triggering errors about "Too many open files" on /etc/...
11
votes
3answers
8k views

How do I compress files in-place?

I have a machine with 90% hard-disk usage. I want to compress its 500+ log files into a smaller new file. However, the hard disk is too small to keep both the original files and the compressed ones. ...
11
votes
3answers
21k views

Execute a command on user logon

In Linux desktop system, I want to execute a command when the user logs in. After reading some other posts, I tried to insert the command in ~/.bashrc but unsuccessfully. Moreover, the system uses a ...
11
votes
3answers
2k views

How do I write all lines from less to a file?

I've piped a command to less, and now I want to save the command's output to a file. How do I do that? In this case, I don't want to use tee, I want a solution directly from less, so that I don't ...
11
votes
2answers
375 views

How to start tailing a file that has not been yet created

I use tail to monitor the progress of jobs that I know will write their progress to disk. Almost always, I know which file they will create before they start running (the jobs are dispatched by a ...
11
votes
7answers
4k views

Shortest way to extract last 3 characters of base (minus suffix) filename

I'm trying to set a variable in an sh script to the last 3 characters of the base name of a file (by base name I mean without the path and without the suffix). I've succeeded in doing this but, purely ...
11
votes
6answers
2k views

Disable Keyboard & Mouse Temporarily

I would like to know how one can disable the keyboard & mouse temporarily in OS X.
11
votes
5answers
2k views

What does “,,,” mean in the 5 column in /etc/passwd file? [duplicate]

There are 7 fields in the /etc/passwd file :username,Password,User ID (UID),Group ID (GID),User ID Info,Home directory,Command/shell. Part of rows in my /etc/passwd : avahi:x:105:110:Avahi mDNS ...
11
votes
3answers
28k views

“echo 3 > /proc/sys/vm/drop_caches” - Permission denied as root

I am currently having some issues with the cache. It is a little too much right now so I wanted to clear it. I googled and found this little command: sync && echo 3 > /proc/sys/vm/...
11
votes
1answer
762 views

Is it possible to use multiple here-docs in bash?

Can one use multiple here-docs to provide input to a command in bash? $ cat <<<foo <<<bar bar $ cat <<EOF1 <<EOF2 > foo > EOF1 > bar > EOF2 bar Obviously, ...
10
votes
2answers
4k views

Should you run automatic updates

I'm running production Centos web servers. I want to know what is best practice for running updates. Should I automate this with yum-cron or yum-updatesd? Or is there a danger of updates breaking ...
10
votes
2answers
4k views

How can I install a 64bit Linux virtual machine on a 32bit Linux?

I've got a computer (Intel core i5) with 32bit Linux installed (ubuntu 11.04) and I would like to install a 64bit Linux virtual machine on it so I can test 64bit command-line applications on it.
10
votes
2answers
5k views

File damaged/lost during transfer? Recovery possible?

I was at uni a few days ago when I attempted to cut and paste a 500Mb file (a 3gp video recording) into my H drive on one of the uni network's Linux (Debian KDE 3.5) computers. I did not see any ...
10
votes
4answers
2k views

How to list all object paths under a dbus service?

This is a follow-up question to A list of available DBus services. The following python code will list all available DBus services. import dbus for service in dbus.SystemBus().list_names(): ...
10
votes
2answers
1k views

grep: display filename once, then display context with line numbers

Our source code has error codes scattered throughout. Finding them is easy with grep, but I'd like a bash function find_code that I can execute (eg. find_code ####) which will provide output along ...
10
votes
2answers
12k views

Local installation of .rpms using YUM

I'm asking this question cautiously because I don't want to get this wrong. I have a program_name.rpm file saved locally on my server (CentOS 6.5). I have installed it previously just by navigating ...
10
votes
3answers
4k views

How can I instruct BSD sed to interpret escape sequences like \n and \t?

I have a sed replacement command that I would like to be compatible with BSD sed as well as GNU sed. Extended regular expressions are not an issue as I do not need them in this case. My primary ...
10
votes
2answers
1k views

Cannot expand asterisk without proper permission

Can someone explain to me the following? $ ls -ld /temp/sit/build/ dr-xr-s--- 3 asdf qwer 4096 Jan 31 2012 /temp/sit/build/ $ ls -ld /temp/sit/build/* ls: /temp/sit/build/*: Permission denied So ...
10
votes
2answers
673 views

Having a problem with a shell script counting characters

I'm trying to learn the basics and I have run into an issue with my script counting the characters of a user's input. Here is my script, can someone point out where I'm going wrong please? #!/bin/...
10
votes
1answer
786 views

Why xterm displays 256 colors (not xterm-256color)?

Could someone explain this? I'm using gnome-terminal. First, some information: # echo $TERM xterm # infocmp xterm Reconstructed via infocmp from file: /lib/terminfo/x/xterm colors#8, cols#80, it#8, ...
10
votes
2answers
3k views

Is there a way to count the number of matches in Vim using :g?

I know this works: :%s/<string>//gn But it seems a bit strange to use the substitution command to count, rather than global..
9
votes
2answers
5k views

find usage with -L

I have link -> file I do find -L . -name 'link' And get ./link Why is that? man find says: -L : Follow symbolic links. When find examines or prints information about files, ...
9
votes
2answers
2k views

How to non-invasively test for write access to a file?

In a shell script, how do I easily and non-invasively test for write access to a file without actually attempting to modify the file? I could parse the output of stat, but that seems really complex, ...
9
votes
5answers
290 views

How can I “stack” shell aliases?

In my .profile (sourced in sh emulation mode from my .zshrc) I have the following snippet: if [ -f /usr/bin/pacmatic ]; then alias pacman=pacmatic fi # Colorized Pacman output alias pacman="...
9
votes
5answers
2k views

Number of characters in a shell command's output

I am writing a script which needs to calculate the number of characters in a command's output in a single step. For example, using the command readlink -f /etc/fstab should return 10 because the ...
9
votes
2answers
2k views

Is the “$?” (dollar-question mark) variable available only in the Bash shell?

In the Bash shell, I can get the command exit status through the $? variable: # ps -ef | grep "haha" root 15439 15345 0 23:02 pts/0 00:00:00 grep --color=auto haha # echo $? 0 Is it ...
9
votes
3answers
332 views

When was process substitution first introduced?

I'm curios to know how long process substitution has been around. What shell first had it? When did it get added to other shells?
9
votes
2answers
192 views

New alias not available after ;

Up to now I thought that a semicolon in the shell has (somehow) the same meaning as a line break. So I was surprised that for alias <name>=<replacement text>; <name> <name> ...
9
votes
6answers
23k views

Using OpenVPN with systemd

Ok, so I've been searching the web for solutions to this problem with no answers seeming to work for me. Hopefully someone can help me. I'm only trying to configure the OpenVPN Client. I'm running ...
9
votes
2answers
6k views

Why does xargs strip quotes from input?

Why does xargs strip quotes from input text? Here is a simplified example: echo "/Place/='http://www.google.com'" | xargs echo outputs /Place/=http://www.google.com Is there any way to work-...
9
votes
3answers
7k views

Why does awk do full buffering when reading from a pipe

I'm reading from a serial port connected to a gps device sending nmea strings. A simplified invocation to illustrate my point: $ awk '{ print $0 }' /dev/ttyPSC9 GPGGA,073651.000,6310.1043,N,...
9
votes
1answer
1k views

Segmentation fault when trying to run glxgears via virtualGL

(Follow-up on How to efficiently use 3D via a remote connection?) I installed the amd64 package on the server and the i386 one on the client. Following the user's guide I run this on the client: me@...
9
votes
1answer
352 views

What's the exact behaviour of the command: ip address change?

I have been fiddling with IPv6 and address lifetimes. I found out that the valid_lft attribute will make a v6-address disappear automagically, if used correctly. To extend an address' lifetime I would ...
9
votes
3answers
766 views

how to check the format of a filesystem

I would like to check, in a bash script, on what filesystem type a directory is. The idea is something like if [path] is on a [filesystem] filesystem then filesystem specific command end if
9
votes
2answers
7k views

How do you specify a format for the input to date?

Given a date and time in a format that is not recognized by date, how can I get date to recognize the date and time? For example: $ date -d "09SEP2012:23:58:46" date: invalid date `09SEP2012:23:58:...
9
votes
4answers
5k views

“Friendly” terminal color names in shell scripts?

I'm aware of libraries in languages such as Ruby and Javascript to make colorizing your terminal scripts easier by using color names like "red". But is there something like this for shell scripts in ...
9
votes
4answers
10k views

How to perform grep on FTP?

I tried searching for similar command in ncftp (actually this is the only terminal ftp client I used) and I didn't find it. What's the way (if possible at all) to use grep command on remote server, ...
9
votes
4answers
18k views

shortest way to replace characters in a variable

There are many ways to replace characters in a variable. The shortest way I found out is tr so far: OUTPUT=a\'b\"c\`d_123and_a_lot_more OUTPUT=$(echo "$OUTPUT"|tr -d "'\`\"") echo $OUTPUT Is ...
9
votes
3answers
15k views

Reset a PCI Device in Linux

Is there a generic way to reset a PCI device in Linux from the command line? That is, cause the PCI bus to issue a reset command.
9
votes
4answers
10k views

How to truely install a tar.gz file on Linux - how to manage manually-installed (or standalone) applications?

I see all these links explaining packages and .debs... I know that... and there are many kludges to get tar.gz files working (eg: update-alternatives for Java or manually dropping the file in /usr/...
9
votes
1answer
8k views

Install g++ when having gcc (C only) — RH6

I have a RHEL 6 machine, which came with gcc but without g++. The gcc version is 4.4.4 20100726 (this is what I got from gcc --version). How can I get g++ working? Currently, the shell just returns "...
9
votes
1answer
4k views

What is the safe way to allow Java 7 to run on SELinux

Short version: What is the most secure way to allow Java 7 to run on (with?) SELinux? Long version: Sorry in advance if I use incorrect terminology. I'm really just a Java developer with a meager ...
9
votes
6answers
5k views

How to find information about the system/machine in Unix?

I have always found it difficult to find information about the system itself in Unix, whether it be Which OS I am using (version number and all, to compare it with the latest available builds)? ...
9
votes
2answers
255 views

How can I conditionally pass a subshell through 'time'?

I have a setup script for a Vagrant box where I used to measure single steps with time. Now I would like to conditionally enable or disable the time measurements. For example, previously a line would ...
9
votes
1answer
9k views

Why the value of VSIZE in top is different from the value of VSZ (Virtual set size) in ps?

I know VSZ in ps is for the total address space allocated for the app and is sometimes aliased as vsize (mentioned in man page of ps on linux), but what's the definition of VSIZE in top? This top ...

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