Shelling Out to Give a System Command Drains Free Memory
I am working on a large program which is always up and must run in as many Linux flavors as possible, i.e. be portable. I have created a number of general utility functions for common tasks it needs to do, and one of these utility functions goes out to the shell to give a Linux command and return the output from the command. Depending on the exact Linux command being performed, occasionally it can drain free memory and not free it immediately.
In one case, I need to call this function to give a shell command and get data back a hundred or so times in a loop, which executes in just a moment. I find that during that loop my free memory decreases dramatically. I presume that it's freed at some point, but during execution of the loop, it can get quite low, and I think it may have caused a program abend in one environment. If you have read this far and are wondering, the command being given is to determine if a service is up, and it does this for every service which has script in /etc/init.d. The command, for bluetooth, for example, is:
service bluetooth status
My question is specifically this, is there anything I can do to my code in this function so that it either uses less memory of frees it better. Here is the code:
I have checked and the character array commandOutputLine[] has no bearing on this problem. How might I re-write this function to make it less of a memory hog or to make it free its memory at once? Thanks in advance.
Reference:
http://story.news.yahoo.com/news?tmpl=story&ncid=738&e=1&u=/ap/20041115/ap_on_hi_te/sun_solaris10
Sun to Give Out Operating System for Free
Mon Nov 15, 7:31 AM ET
By MATTHEW FORDAHL, AP Technology Writer
SAN JOSE, Calif. - After investing roughly $500 million and... (1 Reply)
For example if i have the piece of code as follows:
CountryName = (char *)malloc((strlen(CountryName)+1)*sizeof(char));
memset(CountryName, 0, strlen(CountryName)+1);
CountryName = SOME VALUE
Now how do i free the memory after use of this code???? :confused: (3 Replies)
Hello,
Please can any one explain about the parameters to the write systemcalls??
How are they passed?? and how is the address of the user buffer is handled by the kenel??
for ex: write(fd,buf,count);
How does the kernel handles this user buffer address??
After write does the kernel write... (1 Reply)
Hi,
Im working on Solaris 9 on SPARC-32 bit running on an Ultra-80, and I have to find out the following:-
1. Total Physical Memory in the system(total RAM).
2. Available Physical Memory(i.e. RAM Usage)
3. Total (Logical) Memory in the system
4. Available (Logical) Memory.
I know... (4 Replies)
Hi all,
Could please let me know how to get the more memory free space (not added the RAM) in local zone.
-bash-3.00# vmstat 2 5
kthr memory page disk faults cpu
r b w swap free re mf pi po fr de sr s0 s1 s1 s1 in sy cs us sy... (3 Replies)
Hi Export,
i execute 'top' command to show the free memory in Solaris host, but the read is much lower than the RSS value shown in prstat command. Which one can reflect the real status and it is possible the difference caused by any patch of OS?
Top command (only 883 memory is free)... (3 Replies)
I was running a program and it stopped and showed "Out of Memory!". at that time, the RAM used by this process is around 4G and the free memory size of the machine is around 30G. Does anybody know what maybe the reason? this program is written with Perl. the OS of the machine is Solaris U8. And I... (1 Reply)
Hi guys.
I've a question, if we are using a syscall that receives a string allocated dynamicaly to a determined size, or NUL and it will allocate the apropriate size. We should free the memory or the OS will do it for us?
If a function returns a pointer we should free that poiter when we are done... (7 Replies)
Hi,
I am wondering if there is a way to free up memory in Solaris manually ? the way we can do it in Linux for example :
echo `/bin/date` "************* Memory Info Before *************"
free -m
sync
echo 1 > /proc/sys/vm/drop_caches
echo 2 > /proc/sys/vm/drop_caches
echo 3 >... (13 Replies)
Discussion started by: terrykhatri531
13 Replies
LEARN ABOUT CENTOS
pclose
POPEN(3) Linux Programmer's Manual POPEN(3)NAME
popen, pclose - pipe stream to or from a process
SYNOPSIS
#include <stdio.h>
FILE *popen(const char *command, const char *type);
int pclose(FILE *stream);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
popen(), pclose():
_POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE || _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
The popen() function opens a process by creating a pipe, forking, and invoking the shell. Since a pipe is by definition unidirectional,
the type argument may specify only reading or writing, not both; the resulting stream is correspondingly read-only or write-only.
The command argument is a pointer to a null-terminated string containing a shell command line. This command is passed to /bin/sh using the
-c flag; interpretation, if any, is performed by the shell. The type argument is a pointer to a null-terminated string which must contain
either the letter 'r' for reading or the letter 'w' for writing. Since glibc 2.9, this argument can additionally include the letter 'e',
which causes the close-on-exec flag (FD_CLOEXEC) to be set on the underlying file descriptor; see the description of the O_CLOEXEC flag in
open(2) for reasons why this may be useful.
The return value from popen() is a normal standard I/O stream in all respects save that it must be closed with pclose() rather than
fclose(3). Writing to such a stream writes to the standard input of the command; the command's standard output is the same as that of the
process that called popen(), unless this is altered by the command itself. Conversely, reading from a "popened" stream reads the command's
standard output, and the command's standard input is the same as that of the process that called popen().
Note that output popen() streams are fully buffered by default.
The pclose() function waits for the associated process to terminate and returns the exit status of the command as returned by wait4(2).
RETURN VALUE
The popen() function returns NULL if the fork(2) or pipe(2) calls fail, or if it cannot allocate memory.
The pclose() function returns -1 if wait4(2) returns an error, or some other error is detected. In the event of an error, these functions
set errnro to indicate the cause of the error.
ERRORS
The popen() function does not set errno if memory allocation fails. If the underlying fork(2) or pipe(2) fails, errno is set appropri-
ately. If the type argument is invalid, and this condition is detected, errno is set to EINVAL.
If pclose() cannot obtain the child status, errno is set to ECHILD.
CONFORMING TO
POSIX.1-2001.
The 'e' value for type is a Linux extension.
BUGS
Since the standard input of a command opened for reading shares its seek offset with the process that called popen(), if the original
process has done a buffered read, the command's input position may not be as expected. Similarly, the output from a command opened for
writing may become intermingled with that of the original process. The latter can be avoided by calling fflush(3) before popen().
Failure to execute the shell is indistinguishable from the shell's failure to execute command, or an immediate exit of the command. The
only hint is an exit status of 127.
SEE ALSO sh(1), fork(2), pipe(2), wait4(2), fclose(3), fflush(3), fopen(3), stdio(3), system(3)COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2013-04-19 POPEN(3)