Get kernel information through command line and programatically

By | December 23, 2018

The primary command to get kernel information is uname. The uname command reports basic information about operating system and hardware kernel. For example “name -p” prints the processor type or “unknown”, if it cannot file one.
The “-r” option returns the kernel release version. To get full configuration for currently used kernel run the followung command: “cat /boot/config-$(uname -r)”.
The full information about current kernel may be gotten with “uname -a”:


# uname -a
Linux BAMBOO-209 4.4.0-31-generic #50~14.04.1-Ubuntu SMP Wed Jul 13 01:06:37 UTC 2016 i686 i686 i686 GNU/Linux



Actually uname reads and parses content of /proc/version file, so the same information may be received by reading this file:


# cat /proc/version
Linux version 4.4.0-31-generic (buildd@lgw01-01) (gcc version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04.3) ) #50~14.04.1-Ubuntu SMP Wed Jul 13 01:06:37 UTC 2016

The alternative way to get the same information using sysctl (system control) command:


# sysctl kernel.ostype
kernel.ostype = Linux
# sysctl kernel.osrelease
kernel.osrelease = 4.4.0-31-generic
# sysctl kernel.version
#50~14.04.1-Ubuntu SMP Wed Jul 13 01:06:37 UTC 2016

Now how to get the same kernel data programmatically, through . So sysctl API, file kernctl.cpp:

#include <stdio.h>
#include <sys/types.h>
#include <sys/sysctl.h>
int main(int n, char ** s)
{
  char szBuffer[255];
  size_t length = sizeof(szBuffer);
  int mib[4] = {0,0,0,0};
  size_t miblen = sizeof(mib)/sizeof(int);
  mib[0] = CTL_KERN;
  mib[1] = KERN_OSTYPE;
  int iError = sysctl(mib, 2, &szBuffer, &length, NULL, 0);
  if(iError == 0)
  {
    printf("OS type: %s\n", szBuffer);
  } else {
    printf("Cannot get OS type. Error: %d\n", iError);
  }
  mib[1] = KERN_OSRELEASE;
  length = sizeof(szBuffer);
  iError = sysctl(mib, 2, &szBuffer, &length, NULL, 0);
  if(iError == 0)
  {
    printf("OS release: %s\n", szBuffer);
  } else {
    printf("Cannot get OS release. Error: %d\n", iError);
  }
  mib[1] = KERN_VERSION;
  length = sizeof(szBuffer);
  iError = sysctl(mib, 2, &szBuffer, &length, NULL, 0);
  if(iError == 0)
  {
    printf("OS version and compile time: %s\n", szBuffer);
  } else {
    printf("Cannot get OS version. Error: %d\n", iError);
  }
  return 0;
}

Code testing result:


# g++ -o kernctl.cpp kernctl
# ./kernctl
OS type: Linux
OS release: 4.4.0-31-generic
OS version and compile time: #50~14.04.1-Ubuntu SMP Wed Jul 13 01:06:37 UTC 2016

The sysctl command and API is specifically designed for kernel parameter tuning and may be used to only for reading kernel data and also for changing them.

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