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Reading /proc/stat btime from user space

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  Reading /proc/stat btime from user space SJC <jobhunts02@aol.com> - 2013-01-16 22:37 -0800
    Re: Reading /proc/stat btime from user space Joerg Schmitz-Linneweber <joerg@schmitz-linneweber.name> - 2013-01-17 09:12 +0100
      Re: Reading /proc/stat btime from user space Joerg Schmitz-Linneweber <joerg@schmitz-linneweber.name> - 2013-01-17 09:17 +0100
    Re: Reading /proc/stat btime from user space SJC <jobhunts02@aol.com> - 2013-01-17 10:02 -0800
      Re: Reading /proc/stat btime from user space Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2013-01-17 23:10 +0200
    Re: Reading /proc/stat btime from user space SJC <jobhunts02@aol.com> - 2013-01-17 14:20 -0800
      Re: Reading /proc/stat btime from user space Joerg Schmitz-Linneweber <joerg@schmitz-linneweber.name> - 2013-01-18 16:41 +0100

#432 — Reading /proc/stat btime from user space

I would like to read the value of /proc/stat btime in my user space program.  How can I do that?

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#433

Hi "JobHunter"

Am 17.01.2013 07:37, schrieb SJC:
> I would like to read the value of /proc/stat btime in my user space program.  How can I do that?

btime=$(awk '/btime/ {print $2}')

Of course your "user space prog" is written in sh, right?
:-)

Salut, Joerg

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#434

Ups!

Should read
btime=$(awk '/btime/ {print $2}' /proc/stat)

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#435

On Wednesday, January 16, 2013 10:37:20 PM UTC-8, SJC wrote:
> I would like to read the value of /proc/stat btime in my user space program.  How can I do that?

It is written in C.  How do I get that value into a C variable?

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#436

On 17.1.13 8:02 , SJC wrote:
> On Wednesday, January 16, 2013 10:37:20 PM UTC-8, SJC wrote:
>> I would like to read the value of /proc/stat btime in my user space program.  How can I do that?
>
> It is written in C.  How do I get that value into a C variable?


Are you asking how to read a file from C code?

The /proc pseudo-files read just in the same way as regular files
from the file system.

For details, please re-read your C programming manual.

-- 

Tauno Voipio

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#437

I have a solution (see below).  This will give me, for example, "btime 1358425742."  This is fine because I don't need the actual number.  I just need to compare boottime strings to determine if the system has rebooted.  By the way, if there is a better way to determine if a system has rebooted, please let me know.

static void get_boottime(char *boottime) {

        FILE *fp;
        int status;

        fp = popen("awk '/^btime/' /proc/stat", "r");
        if (fp == NULL) {
                DEBUG("get_boottime: popen failed");
        }
        else {
                fgets(boottime, BOOTTIME_MAX_LEN, fp);
                DEBUG("get_boottime: Boottime is %s", boottime);
                status = pclose(fp);
                if (status == -1) {
                        DEBUG("get_boottime: Could not close");
                }
        }
        return;
}

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#438

Hi!

Am 17.01.2013 23:20, schrieb SJC:
> static void get_boottime(char *boottime) {
> 
>         FILE *fp;
>         int status;
> 
>         fp = popen("awk '/^btime/' /proc/stat", "r");
>         if (fp == NULL) {
>                 DEBUG("get_boottime: popen failed");
>         }
>         else {
>                 fgets(boottime, BOOTTIME_MAX_LEN, fp);
>                 DEBUG("get_boottime: Boottime is %s", boottime);
>                 status = pclose(fp);
>                 if (status == -1) {
>                         DEBUG("get_boottime: Could not close");
>                 }
>         }
>         return;
> }
You're kidding, aren't you? :-)

Why not read in the file line-by-line and check if the actual line
starts with 'btime'? (fopen, fgets, strncmp, fclose)

You are starting a new process and creating two pipes to read something
from a (text) file?

Perhaps Tauno's tip was more suitable... ;-)

Salut, Jörg

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