diff --git a/6/etc/group.c b/6/etc/group.c
new file mode 100644
index 0000000..15167bb
--- /dev/null
+++ b/6/etc/group.c
@@ -0,0 +1,25 @@
+#include <grp.h>
+#include <stdio.h>
+
+int main(void){
+  
+  struct group *p_gp = getgrnam("sudo");
+  
+  if(p_gp == NULL) {
+    printf("getgrgid error\n");
+    return -1;
+  }
+
+  printf("%d %s", p_gp->gr_gid, p_gp->gr_name);
+
+  char **p_men = p_gp->gr_mem;
+
+  while(*p_men != NULL){
+    printf(" %s", *p_men);
+    p_men++;
+  }
+
+  printf("\n");
+
+  return 0;
+}
diff --git a/6/etc/pwd.c b/6/etc/pwd.c
new file mode 100644
index 0000000..a20d87f
--- /dev/null
+++ b/6/etc/pwd.c
@@ -0,0 +1,19 @@
+#include <pwd.h>
+#include <stdio.h>
+
+
+int main(void) {
+  
+  struct passwd *p_pwd = getpwnam("eric");
+
+  printf("%d %d %s %s %s\n", p_pwd->pw_uid, p_pwd->pw_gid, p_pwd->pw_name, p_pwd->pw_shell, p_pwd->pw_passwd);
+
+
+  while((p_pwd = getpwent()) != NULL) {
+    printf("%d %d %s %s\n", p_pwd->pw_uid, p_pwd->pw_gid, p_pwd->pw_name, p_pwd->pw_shell);
+  }
+
+  endpwent();
+  
+  return 0;
+}
diff --git a/6/etc/spwd.c b/6/etc/spwd.c
new file mode 100644
index 0000000..9fdb1e6
--- /dev/null
+++ b/6/etc/spwd.c
@@ -0,0 +1,14 @@
+#include <shadow.h>
+#include <stdio.h>
+
+int main(void) {
+  struct spwd *p_spwd = getspnam("eric");
+  
+  printf("%s %s %ld %lu\n", p_spwd->sp_namp, p_spwd->sp_pwdp, p_spwd->sp_flag, p_spwd->sp_max);
+
+  printf("%ld %ld %ld\n", p_spwd->sp_min, p_spwd->sp_inact, p_spwd->sp_warn);
+
+  endspent();
+
+  return 0;
+}
diff --git a/6/etc/uname.c b/6/etc/uname.c
new file mode 100644
index 0000000..dc678c2
--- /dev/null
+++ b/6/etc/uname.c
@@ -0,0 +1,15 @@
+#include <sys/utsname.h>
+#include <stdio.h>
+
+int main(void) {
+  struct utsname utsn;
+
+  if(uname(&utsn) < 0) {
+    printf("uname error\n");
+    return -1;
+  }
+
+  printf("%s %s %s %s\n", utsn.sysname, utsn.nodename, utsn.machine, utsn.release);
+  printf("%s\n", utsn.version);
+  return 0;
+}
diff --git a/6/time/clock.c b/6/time/clock.c
new file mode 100644
index 0000000..2925c4f
--- /dev/null
+++ b/6/time/clock.c
@@ -0,0 +1,36 @@
+#include <sys/time.h>
+#include <time.h>
+#include <stdio.h>
+
+int main(void) {
+  struct timespec tsp;
+  if(clock_gettime(CLOCK_REALTIME, &tsp) < 0) {
+   printf("clock_gettime error\n");
+   return -1;
+  }
+
+  printf("real time: %lu %lu\n", tsp.tv_sec, tsp.tv_nsec);;
+
+  if(clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &tsp) < 0) {
+   printf("clock_gettime error\n");
+   return -1;
+  }
+   
+  printf("cpu time: %lu %lu\n", tsp.tv_sec, tsp.tv_nsec);;
+
+  if(clock_gettime(CLOCK_THREAD_CPUTIME_ID, &tsp) < 0) {
+   printf("clock_gettime error\n");
+   return -1;
+  }
+   
+  printf("thread time: %lu %lu\n", tsp.tv_sec, tsp.tv_nsec);;
+
+  if(clock_getres(CLOCK_REALTIME, &tsp) < 0) {
+    printf("clock_getres error\n");
+    return -1;
+  }
+
+  printf("real time res: %lu %lu\n", tsp.tv_sec, tsp.tv_nsec);;
+
+  return 0;
+}
diff --git a/6/time/format.c b/6/time/format.c
new file mode 100644
index 0000000..7ab59b1
--- /dev/null
+++ b/6/time/format.c
@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <time.h>
+
+
+void printTm(struct tm *ptm) {
+  printf("%d-%d-%d\n", 1900 + ptm->tm_year, 1 + ptm->tm_mon, ptm->tm_mday);
+  printf("%d:%d:%d\n", ptm->tm_hour, ptm->tm_min, ptm->tm_sec);
+  printf("\n");
+}
+
+int main(void) {
+  time_t t = time(NULL);
+  struct tm * ptm = gmtime(&t);
+
+  printTm(ptm);
+
+  ptm = localtime(&t);
+
+  printTm(ptm);
+
+  t = mktime(ptm);
+
+  printf("time: %lu\n", t);
+
+  char buf[1024];
+
+  size_t wbit = strftime(buf , sizeof(buf), "%D %T  %r %Z", ptm);
+
+  if(wbit == 0) {
+    printf("strftime error\n");
+    return -1;
+  }
+
+  printf("format: %s\n", buf);
+
+  sprintf(buf, "09/04/00 1:00:00");
+
+  strptime((const char *)buf, "%x %X", ptm);
+
+  wbit = strftime(buf , sizeof(buf), "%D %T  %r %Z", ptm);
+
+  if(wbit == 0) {
+    printf("strftime error\n");
+    return -1;
+  }
+
+  printf("check format: %s\n", buf);
+  
+  return 0;
+}
diff --git a/6/time/time.c b/6/time/time.c
new file mode 100644
index 0000000..3ec2e70
--- /dev/null
+++ b/6/time/time.c
@@ -0,0 +1,8 @@
+#include <time.h>
+#include <stdio.h>
+
+int main(void) {
+  time_t t = time(NULL);
+  printf("%lu\n", t);
+  return 0;
+}