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4
votes
2answers
91 views

Process substitution from curl to bash as root

I'm trying to run a script from URL as root with this command: sudo bash <(curl -s http://copy.com/gLVZIqUubzcS/popcorn) But I'm getting this error: bash: /dev/fd/63: Aucun fichier ou dossier ...
4
votes
2answers
39 views

Portability of file descriptor links

I've always wondered this but never took the time to find out, so I'll do so now - how portable is the usage shown here of either /proc/$$/fd/$N or /dev/fd/$N? I understand POSIX guarantees /dev/null, ...
2
votes
4answers
70 views

Can a running script identify the logging context?

Let us say I redirect the STDOUT, STDERR of a program to files. ./script.sh 1> output.log 2> error.log Can the running program find this out i.e. know the paths to these files?
2
votes
2answers
75 views

Close all file descriptors in bash

Is there a way to close all the open file descriptors, without having an explicit list of them beforehand?
2
votes
3answers
79 views

Redirecting only stderr to a pipe

This code snippet is from Advanced Bash Scripting Guide. # Redirecting only stderr to a pipe. exec 3>&1 # Save current "value" of stdout. ls -l 2>&1 ...
3
votes
1answer
86 views

What does exec 3<&1 do?

I understand exec can do I/O Redirection on current shell level. but I only sees usage like exec 6<&0 # Link file descriptor #6 with stdin. # Saves stdin. exec 6>&1 # ...
0
votes
2answers
54 views

How to reset the file descriptor

I was trying to use file descriptor for printing the lines in the file #!/usr/bin/ksh exec 3<&0 exec 0< file.txt while read LINE do echo “$LINE” done and I am done with my code ,it ...
4
votes
3answers
198 views

Please help explain this bash output redirection

This script was posted as answer to a Question. And I'm trying to work out what's going on. result=$( { { ssh host app-status >&3 3>&-; echo "$?" } | { until read ...
3
votes
1answer
58 views

What is the relationship between a program's output, standard output, and its file descriptors?

Let's assume that I am running wget which is downloading something. It's printing some text to my terminal and writes the downloaded data into a file. From a terminology point of view, what is the ...
1
vote
0answers
60 views

Which socket is gnome-shell reading from continuously?

strace shows that the GNOME shell is continuously trying to read from a socket, which is often not available (or doesn't contain any data to read from): strace -p gnome-shell-pid -e trace=recvfrom ...
12
votes
2answers
154 views

Output order with process substitution

This is what I usually do to run grep and wc on a file without having to scan it twice <file.txt tee >(grep LITERAL) >(wc -l) >/dev/null However, this yields EXEC LITERAL 32 ...
4
votes
2answers
207 views

Does OpenBSD have a limit to the number of file descriptors?

What's the maximum number of file descriptors that a process can get on OpenBSD successfully? For example, there is an openfiles limit in login.conf(5) in OpenBSD. If I want to have as many file ...
1
vote
3answers
60 views

Print a message from the left-hand side of a pipe

I want to use a variable from the main shell in a sub shell. I did: export mysql_root_password="test" ( echo $mysql_root_password ) | dialog --gauge "Working hard..." 6 50 But it does not ...
4
votes
1answer
150 views

Why doesn't the process substitution <() work with ssh -F

I have some vagrant virtual machines. To log into them I issue the vagrant ssh command. I want to log into them using regular ssh command. The vagrant ssh-config outputs the suitable config file $ ...
2
votes
2answers
150 views

AIX open() : file descriptor is zero (!?)

A daemon process, on detecting the presence of a text file in a particular directory then launches an executable file which opens the aforementioned text file in order to read and then transmit its ...
0
votes
0answers
150 views

Embedded device GadgetFS connects to Linux machine and receives one USB setup request more than with a windows machine connected

I am using this GadgetFS implementation http://www.linux-usb.org/gadget/usb.c to have my embedded device connect to a Host. What's weird is, when I connect it to a Windows machine everything works ...
5
votes
1answer
86 views

Replacing stdout with stderr

Is it possible to redirect the output from a command to replace the text sent to stdout with the text from stderr? $ ./script this line is redirected to stdout this line is redirected to stderr $ ...
2
votes
1answer
325 views

File descriptor and fork

When a child is forked then it inherits parent's file descriptors, if child closes the file descriptor what will happen ? If child starts writing what shall happen to the file at the parent's end ? ...
4
votes
1answer
852 views

How to circumvent “Too many open files” in debian

If I want to see all relevant log files of my apache2 server at once, I use tail -f /var/kunden/logs/*log /var/kunden/logs/*log /var/log/apache2/*log |grep -v robots|grep -v favicon But since those ...
5
votes
1answer
275 views

Limits on the number of file descriptors

I'm trying to install 389-ds, And it gives me this warning : WARNING: There are only 1024 file descriptors (hard limit) available, which limit the number of simultaneous connections. I understand ...
2
votes
1answer
750 views

How to find speed of wlan interface?

I'm trying to find speed of network interface using file-descriptor. It's easy to do it for ethX, just calling cat /sys/class/net/eth0/speed. Unfortunately this method doesn't work with wireless ...
3
votes
2answers
229 views

Cross-process dup on Linux

I'd like to dup a file descriptor running in an unrelated process on Linux. I know about sendmsg(2) and SCM_RIGHTS (e.g. ...
4
votes
3answers
613 views

Something's special about /dev/fd/3

I've been trying to learn about file descriptors. When I type "ls -l /dev/fd/" I get lrwx------ 1 me users 64 May 2 16:02 0 -> /dev/pts/5 l-wx------ 1 me users 64 May 2 16:02 1 -> ...
1
vote
3answers
606 views

How to check which process is using a given file descriptor?

Somewhere in the middle of my application, the framework I'm using (ROOT) gives me the following error: *** Break *** write on a pipe with no one to read it SysError in ...
2
votes
1answer
189 views

open() console for default file descriptors

I'm reading a shell program implementation in C ( the xv6 shell from MIT's 6.828 Operating System Engineering course ). The main() function for this shell starts with the following code: //Assumes ...
3
votes
2answers
5k views

Difference between 2>&-, 2>/dev/null, |&, &>/dev/null and >/dev/null 2>&1

Just looking for the difference between 2>&- 2>/dev/null |& &>/dev/null >/dev/null 2>&1 and their portability with non-Bourne shells like tcsh, mksh, etc.
0
votes
1answer
175 views

Understand Fd`s and nodejs

I'm having a bit of a confused time understanding what a file descriptor is and if I even need one! I am trying to spawn a process in nodejs and have its out put be written directly to an out put ...
2
votes
1answer
100 views

Why is it possible to refer to a closed stderr under bash?

I'd like to know why bash doesn't display an error message when we refer to a closed stderr. When it comes to other file descriptors, they have to be opened if we want to, for example, duplicate them. ...
8
votes
3answers
552 views

Practical use for moving file descriptors

According to the bash man page: The redirection operator [n]<&digit- moves the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n is ...
3
votes
1answer
201 views

Significance of arrows symbols in duplicating/closing file descriptors under bash

I'm reading a book about Linux command line where author doesn't seem to follow the conventions in bash manual regarding arrows symbols used in redirection operations. Namely, he always uses left ...
2
votes
2answers
461 views

What sets a child's STDERR, STDOUT, and STDIN?

If a program runs fork() what sets standard streams STDOUT, STDIN and STDERR?
0
votes
2answers
167 views

Why doesn't Bash accept `&>&3`, i.e. redirecting stdout and stderr to file descriptor 3?

Given the preamble, foobar function and invocations of it: exec 3>/dev/null function foobar { echo foo; echo bar >&2; } foobar >/dev/null foobar 2>/dev/null foobar ...
2
votes
1answer
60 views

How is the inherited file descritor vulnerability dealt with in Unices?

Ulrich Drepper describes a vulnerability in programs that have open file descriptors then they fork() and execve() without lots of very careful locking in place. He also talks about new kernel ...
2
votes
2answers
162 views

Where to place a Bash shell redirection for a command? [duplicate]

Possible Duplicate: Order of redirections Apart from the standalone exec >&2 to redirect the current shell's input and output are there any behavioral differences in the following ...
4
votes
1answer
369 views

Timestamp of socket in /proc/<pid>/fd

If I list /proc/<pid>/fd I see a number of entries for sockets. These entries have timestamps. At first I thought they were when the socket was created. But it doesn't always appear to be the ...
2
votes
1answer
125 views

Max Open Files, clarification needed

On my machine, ulimit -n returns 2560 Given that -n returns The maximum number of open file descriptors. Does it mean that system won't allow more then 2560 open files to be out there at any ...
2
votes
1answer
443 views

Parameretrize file descriptor number to open a tcp socket in shell script

I'm tried to parameretrize in a variable the file descriptor number to open a tcp socket using exec command but it failed. Only work correctly when file descriptor number is a constant. In the next ...
2
votes
2answers
2k views

What are the dangers of setting a high limit to max File Descriptors per process?

I'm working on an old legacy application, and I commonly come across certain settings that no one around cam explain. Apparently at some point, some processes in the application were hitting the max ...
5
votes
1answer
1k views

What is the file descriptor 3 assigned by default?

$ ls -og /proc/self /proc/self/fd lrwxrwxrwx 1 64 Jun 18 11:12 /proc/self -> 32157 /proc/self/fd: total 0 lrwx------ 1 64 Jun 22 2012 0 -> /dev/tty1 lrwx------ 1 64 Jun 22 2012 1 -> ...
6
votes
2answers
3k views

Execute command in remote active terminal

Suppose you have a terminal emulator (T1) open with a PID of 6350. From another terminal, type this command (C1): echo "ls\n" > /proc/6350/fd/0 This writes ls and the new line in T1 but does ...
2
votes
1answer
240 views

Why doesnt ctrl+d work with this?

I wanted a simple way to process text in my clipboard without having to create a file. I tried using the following line: awk '{print $1}' <(cat) but I couldn't send cat the EOF character using ...
10
votes
2answers
344 views

Order of redirections

I don't quite understand how the computer reads this command. cat file1 file2 1> file.txt 2>&1 If I understand, 2>&1 simply redirect Standard Error to Standard Output. By that ...
14
votes
2answers
936 views

Portability of “> /dev/stdout”

Occasionally I need to specify a "path-equivalent" of one of the standard IO streams (stdin, stdout, stderr). Since 99% of the time I work with Linux, I just prepend /dev/ to get /dev/stdin, etc., ...
5
votes
1answer
380 views

Why does reading from two connected pty's cause an infinite loop?

I want to fake a gsm modem for testing a program. I want the program to send AT-codes to me and that I can answer it back, kind of a VirtualSerialPort. But for some reason the data written from the ...
8
votes
4answers
2k views

How can same fd in different processes point to the same file?

Say I have process 1 and process 2. Both have a file descriptor corresponding to the integer 4. In each process however the file descriptor 4 points to a totally different file in the Open File Table ...
9
votes
2answers
2k views

What happens when I close() a file descriptor?

I am trying to get the whole picture with file descriptors. Say I have process1 which initially has these file descriptors: _process1_ | | | 0 stdin | | 1 stdout | | 2 stderr | ...
5
votes
0answers
97 views

How can different file descriptors point to the same file in open file table? [duplicate]

Possible Duplicate: How can same fd in different processes point to the same file? I have a hard time grasping the two ideas of File Descriptor Table and Open File Table. Open File Table ...
20
votes
3answers
3k views

When would you use an additional file descriptor?

I know you can create a file descriptor and redirect output to it. e.g. exec 3<> /tmp/foo # open fd 3. echo a >&3 # write to it exec 3>&- # close fd 3. But you can do the same ...
4
votes
2answers
737 views

file descriptor vs. file name

I was wondering what differences and relations are between file descriptors and file names. Are they all used to access files? If yes, in the same way? For example, /dev/fd/0, /dev/stdin, and ...
9
votes
3answers
3k 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 ...