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Commit a9ac7af

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Added examples of working with other process attributes.
1 parent 70cb8eb commit a9ac7af

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3 files changed

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3 files changed

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‎multithreading/01 - Env Vars.c

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#include <stdio.h>
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#include <stdlib.h>
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#include "Common.h"
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extern char ** environ; // Global variable availble to any process for read/write.
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#define ENVVARSAPP "ENVVARSAPP=test"
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#define OVERWRITE 1
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// Compilation:
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// gcc -std=gnu99 "01 - Env Vars.c" -o envVars
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// Task:
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// Read, write environment variables.
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int main(int argc, char *argv[])
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{
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printf("Variables available process:\n");
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for (int i = 0; environ[i] != NULL; i++)
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{
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printf("%s\n", environ[i]);
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}
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// Get HOME variable
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char *s = getenv("HOME");
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if (s == NULL)
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{
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printf("HOME not found.\n");
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}
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else
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{
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printf("Value of HOME: \"%s\"\n", s);
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}
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// Put new variable.
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// WARNING! Don't put local or automatic non-static variables since it will be used by system.
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if (putenv(ENVVARSAPP) == FAILURE)
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{
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perror("putenv ENVVARSAPP failed!\n");
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}
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else
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{
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printf("putenv ENVVARSAPP succeeded!\n");
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}
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// Set new variable.
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if (setenv("ENVVARSAPP2", "test2", OVERWRITE) == FAILURE)
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{
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perror("setenv ENVVARSAPP2 failed!\n");
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}
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else
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{
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printf("setenv ENVVARSAPP2 succeeded!\n");
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}
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// Remove variables.
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if (unsetenv("ENVVARSAPP") == FAILURE)
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{
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perror("unsetenv ENVVARSAPP failed!\n");
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}
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else
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{
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printf("unsetenv ENVVARSAPP succeeded!\n");
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}
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if (unsetenv("ENVVARSAPP2") == FAILURE)
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{
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perror("unsetenv ENVVARSAPP2 failed!\n");
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}
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else
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{
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printf("unsetenv ENVVARSAPP2 succeeded!\n");
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}
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printf("Exit process!\n");
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exit(EXIT_SUCCESS);
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}
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#include <stdio.h>
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#include <stdlib.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <sys/wait.h> // For wait, waitpid
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#include "Common.h"
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// Compilation:
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// gcc -std=gnu99 "02 - Parent Process Die.c" -o parentDie
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// Task:
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// Use fork to create a child process. Emulate parent process died and Parent PID should become Init (1) or some other?
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const char* get_process_name_by_pid(const int pid)
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{
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char* name = (char*)calloc(1024,sizeof(char));
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if(name)
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{
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sprintf(name, "/proc/%d/cmdline",pid);
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FILE* f = fopen(name,"r");
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if(f)
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{
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size_t size;
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size = fread(name, sizeof(char), 1024, f);
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if(size>0)
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{
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if('\n'==name[size-1])
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{
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name[size-1]='0円';
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}
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}
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fclose(f);
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}
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}
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return name;
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}
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int main(int argc, char *argv[])
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{
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printf("Enter to main!\n");
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printf("Create 1 child process...\n");
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pid_t pid;
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int status;
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switch(pid=fork())
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{
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case -1:
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perror("1 Error of calling fork");
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exit(EXIT_FAILURE);
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case 0:
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printf("1 CHILD: Child process %d!\n", getpid());
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printf("2 CHILD: Parent PID %d!\n", getppid());
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printf("3 CHILD: Wait 3 seconds...\n");
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sleep(3);
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pid_t ppid = getppid();
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printf("4 CHILD: Looks like PARENT died! What is my parent pid? %d\n", ppid); // TODO Find Parent Process Name.
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printf("5 CHILD: My parent now is: %s\n", get_process_name_by_pid(ppid)); // TODO Find Parent Process Name.
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printf("6 CHILD: Wow! Cool! Exit!\n");
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exit(EXIT_SUCCESS);
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default:
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printf("1 PARENT: Parent process %d!\n", getpid());
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printf("2 PARENT: Child PID %d\n", pid);
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printf("3 PARENT: Wait 2 seconds...\n");
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sleep(2);
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printf("4 PARENT: Dying... bye-bye child process!\n");
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}
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}
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#include <stdio.h>
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#include <stdlib.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <sys/wait.h> // For wait, waitpid
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#include "Common.h"
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// Compilation:
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// gcc -std=gnu99 "03 - Process attributes.c" -o processAttrs
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// Task:
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// Work with process attributes.
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int main(int argc, char *argv[])
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{
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printf("Enter to main!\n");
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printf("Create 1 child process...\n");
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pid_t pid;
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int status;
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switch(pid=fork())
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{
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case -1:
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perror("1 Error of calling fork");
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exit(EXIT_FAILURE);
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case 0:
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printf("1 CHILD: Child process %d!\n", getpid());
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printf("2 CHILD: Parent PID %d!\n", getppid());
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printf("3 CHILD: Who created me? User ID: %d\n", getuid());
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printf("3 CHILD: Who created me? Effective User ID: %d\n", geteuid());
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printf("3 CHILD: Who created me? Group ID: %d\n", getgid());
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printf("3 CHILD: Who created me? Effective Group ID: %d\n", getegid());
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// WARNING!! Works only under ROOT.
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// Changing root from / to some another directory (Example: restrict access to directories more than Web Server directories for Security).
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//printf("4 CHILD: Let's change Working Dir: %d\n", chdir(""));
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//printf("4 CHILD: Let's change Working Dir: %d\n", fchdir(""));
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//printf("4 CHILD: Let's change Root Dir: %d\n", chroot(""));
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// Process priority is in range N=[0, 39]. Nice returns N-20. In case of error Nice returns -1. If N == 19 ir returns -1 TOO :).
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printf("5 CHILD: Let's decrease Priority Level for N=5: %d (N-20)\n", nice(5));
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printf("5 CHILD: Let's increase Priority Level for N=-5: %d (N-20)\n", nice(-5));
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printf("6 CHILD: Wait 4 seconds...\n");
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sleep(4);
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printf("7 CHILD: Exit!\n");
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exit(EXIT_FAILURE);
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default:
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printf("1 PARENT: Parent process %d!\n", getpid());
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printf("2 PARENT: Child PID %d\n", pid);
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printf("3 PARENT: Who created me? User ID: %d\n", getuid());
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printf("3 PARENT: Who created me? Group ID: %d\n", getgid());
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printf("3 PARENT: Who created me? Effective (under which permissions) User ID: %d\n", geteuid());
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printf("3 PARENT: Who created me? Effective (under which permissions) Group ID: %d\n", getegid());
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waitpid(pid, &status, 0);
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printf("4 PARENT: Child exit code: %d\n", WEXITSTATUS(status));
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printf("5 PARENT: Exit!\n");
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}
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printf("Exit process!\n");
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exit(EXIT_SUCCESS);
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}

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