diff --git a/2/limits/.isoc.c.swp b/2/limits/.isoc.c.swp
new file mode 100644
index 0000000..8c9c729
Binary files /dev/null and b/2/limits/.isoc.c.swp differ
diff --git a/2/limits/conf.c b/2/limits/conf.c
new file mode 100644
index 0000000..b526e5e
--- /dev/null
+++ b/2/limits/conf.c
@@ -0,0 +1,39 @@
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+
+extern int errno;
+
+static long posix_version = 0;
+
+static long xsi_version = 0;
+
+int main(void) {
+
+  // get interface version
+  posix_version = sysconf(_SC_VERSION);
+  xsi_version = sysconf(_SC_XOPEN_VERSION);
+
+  printf("%ld %ld\n", posix_version, xsi_version);
+
+  // sysconf
+  printf("%ld\n", sysconf(_SC_ARG_MAX));
+  printf("%ld %ld\n", sysconf(_SC_CHILD_MAX), sysconf(_SC_CLK_TCK));
+  printf("%ld %ld\n", sysconf(_SC_LOGIN_NAME_MAX), sysconf(_SC_OPEN_MAX));
+  printf("%ld\n", sysconf(_SC_SEM_NSEMS_MAX));
+
+  if(!~sysconf(_SC_SEM_NSEMS_MAX) && errno == EINVAL){
+    printf("Not a proper value.\n");
+  } 
+
+  printf("%ld %ld\n", sysconf(_SC_TIMER_MAX), sysconf(_SC_STREAM_MAX));
+
+  // pathconf
+  printf("%ld\n", pathconf("./conf.c", _PC_FILESIZEBITS));
+  printf("%ld\n", pathconf("./conf.c", _PC_NAME_MAX));
+  // printf("%ld\n", pathconf("./conf.c", _PC_TIMESTAMP_RESOLUTION));
+  printf("%ld\n", pathconf("./conf.c", _PC_PATH_MAX));
+  printf("%ld\n", pathconf("./conf.c", _PC_LINK_MAX));
+
+  return 0;
+}
diff --git a/2/limits/isoc.c b/2/limits/isoc.c
index e7b4062..77305d1 100644
--- a/2/limits/isoc.c
+++ b/2/limits/isoc.c
@@ -2,12 +2,22 @@
 #include <stdio.h>
 
 int main(void){
+  // char
   printf("%d %d %d\n", CHAR_BIT, CHAR_MAX, CHAR_MIN);
+  // signed char
+  printf("%d %d\n", SCHAR_MAX, SCHAR_MIN);
+  // unsigned char
+  printf("%d\n", UCHAR_MAX);
+  // int
   printf("%d %d\n", INT_MAX, INT_MIN);
+  // short
   printf("%d %d\n", SHRT_MAX, SHRT_MIN);
+  // long
   printf("%ld %ld\n", LONG_MAX, LONG_MIN);
+  // long long
   printf("%lld %lld\n", LLONG_MAX, LLONG_MIN);
-
+  // extra
   printf("%d %d %d\n", FOPEN_MAX, TMP_MAX, FILENAME_MAX);
+
   return 0;
 }
diff --git a/2/limits/openmax.c b/2/limits/openmax.c
new file mode 100644
index 0000000..9a37a49
--- /dev/null
+++ b/2/limits/openmax.c
@@ -0,0 +1,28 @@
+#include <errno.h>
+#include <limits.h>
+#include <unistd.h>
+#include <stdio.h>
+
+#ifdef OPEN_MAX
+static long openmax = OPEN_MAX;
+#else
+static long openmax = 0;
+#endif
+
+#define OPEN_MAX_GUESS 256
+
+int main(void){
+
+  if(openmax == 0) { 
+    errno = 0;
+    if((openmax = sysconf(_SC_OPEN_MAX)) < 0){
+       if(errno == 0)
+        openmax = OPEN_MAX_GUESS;
+       else
+        printf("sysconf error for _SC_OPEN_MAX");
+    }
+  }
+
+  printf("%ld\n", openmax);
+
+}
diff --git a/2/limits/options.c b/2/limits/options.c
new file mode 100644
index 0000000..15d9216
--- /dev/null
+++ b/2/limits/options.c
@@ -0,0 +1,24 @@
+#include <errno.h>
+#include <unistd.h>
+#include <stdio.h>
+
+
+int main(void){
+
+  printf("%ld %d %d\n", _POSIX_ASYNCHRONOUS_IO, _POSIX_JOB_CONTROL, _POSIX_SHELL);
+  printf("%ld %ld %ld\n", _POSIX_SPIN_LOCKS, _POSIX_THREADS, _POSIX_TIMERS);
+  printf("%d %ld %d\n", _XOPEN_REALTIME, sysconf(_SC_XOPEN_CRYPT), _XOPEN_SHM);
+
+  if(errno != 0){
+    printf("sysconf error for _SC_XOPEN_CRYPT\n");
+  }
+
+  printf("%ld\n", pathconf("./openmax.c", _PC_ASYNC_IO));
+  if(errno != 0){
+    printf("sysconf error for _PC_ASYNC_IO\n");
+  }
+
+  printf("%ld\n", pathconf("./openmax.c", _PC_CHOWN_RESTRICTED));
+
+  return 0;
+}
diff --git a/2/limits/posix.c b/2/limits/posix.c
new file mode 100644
index 0000000..a11e3b9
--- /dev/null
+++ b/2/limits/posix.c
@@ -0,0 +1,22 @@
+#include <limits.h>
+#include <stdio.h>
+
+int main(void){
+  
+  // the length of the args of exec()
+  printf("%d\n", _POSIX_ARG_MAX);
+  // the num of child process under a real user id
+  printf("%d\n", _POSIX_CHILD_MAX);
+  // some var about file and path
+  printf("%d %d %d\n", _POSIX_OPEN_MAX, _POSIX_NAME_MAX, _POSIX_PATH_MAX);
+  // something further
+  printf("%d %d %d\n", _POSIX_LOGIN_NAME_MAX, _POSIX_MAX_CANON, _POSIX_MAX_INPUT);
+  // more
+  printf("%d %d %d\n", _POSIX_SSIZE_MAX, _POSIX_SEM_NSEMS_MAX, _POSIX_TIMER_MAX);
+ 
+  // different between the real value and define value
+  printf("%d %d\n", _POSIX_TTY_NAME_MAX, TTY_NAME_MAX);
+
+  return 0;
+}
+
diff --git a/2/limits/xsi.c b/2/limits/xsi.c
new file mode 100644
index 0000000..e92d05f
--- /dev/null
+++ b/2/limits/xsi.c
@@ -0,0 +1,7 @@
+#include <limits.h>
+#include <stdio.h>
+
+int main(void) {
+  printf("%d\n", NZERO);
+  return 0;
+}