diff --git a/3/file/fileappend.c b/3/file/fileappend.c
new file mode 100644
index 0000000..7b27020
--- /dev/null
+++ b/3/file/fileappend.c
@@ -0,0 +1,46 @@
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdio.h>
+
+int readFile(int fd){
+
+  char buff[1024];
+
+  ssize_t rbit = pread(fd, buff, 1024, 0);
+  
+  if(rbit < 0){
+    printf("Error in reading file\n");
+    return -1;
+  }
+  
+  buff[rbit] = '\0';
+
+  printf("rbit: %ld %s\n", rbit, buff);
+
+  return 0;
+
+}
+
+int main(void){
+  int fd = open("./test/fileat", O_RDWR | O_SYNC);
+
+  if(fd < 0){
+    printf("Error in opening file fileat.\n");
+    return -1;
+  }
+  
+  readFile(fd);
+
+  ssize_t wbit = pwrite(fd, "How", 3, 0);
+
+  if(wbit < 0) {
+    printf("Error in writing file.\n");
+    return -1;
+  }
+
+  readFile(fd);
+
+  close(fd);
+
+  return 0;
+}
diff --git a/3/file/filecntl.c b/3/file/filecntl.c
new file mode 100644
index 0000000..c4bd681
--- /dev/null
+++ b/3/file/filecntl.c
@@ -0,0 +1,30 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+int getFL(int fd) { return fcntl(fd, F_GETFL, 0); }
+
+int main(void) {
+  int fd = open("./test/fileat", O_RDWR);
+
+  printf("FL: %d\n", getFL(fd));
+
+  if (fcntl(fd, F_SETFL, getFL(fd) |  O_APPEND) < 0) {
+    printf("fcntl F_SETFL error\n");
+    return -1;
+  }
+
+  printf("FL: %d\n", getFL(fd));
+
+  char buff[] = "Nope";
+  int wbit = write(fd, buff, sizeof(buff));
+
+  if (wbit < 0) {
+    printf("write buff error\n");
+    return -1;
+  }
+
+  close(fd);
+
+  return 0;
+}
diff --git a/3/file/filedup.c b/3/file/filedup.c
new file mode 100644
index 0000000..aab20ce
--- /dev/null
+++ b/3/file/filedup.c
@@ -0,0 +1,31 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+int main(void) {
+  int fd = open("./test/fileat", O_RDWR | O_SYNC);
+
+  int fd2 = dup(fd);
+
+  off_t off = lseek(fd, 3, SEEK_SET);
+
+  if (off == -1) {
+    printf("Fail to call lseek\n");
+    return -1;
+  }
+
+  char buff[1024];
+
+  int rbit = read(fd2, buff, 1024);
+
+  if (rbit < 0) {
+    printf("Error in reading file fileat");
+    return -1;
+  }
+
+  buff[rbit] = 0;
+
+  printf("rbit: %ld %s\n", rbit, buff);
+
+  return 0;
+}
diff --git a/3/file/filerw.c b/3/file/filerw.c
new file mode 100644
index 0000000..8b06d01
--- /dev/null
+++ b/3/file/filerw.c
@@ -0,0 +1,33 @@
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdio.h>
+
+int main(void){
+  int fd = open("./test/fileat", O_RDWR | O_SYNC);
+  
+  if(fd == -1){
+    printf("Error in opening file fileat.\n");
+  }
+
+  char buff[1024];
+
+  ssize_t rbit = read(fd, buff, 1024);
+
+  if(rbit > 0)
+    buff[rbit] = '\0';
+
+  printf("%ld %s\n", rbit, buff);
+
+  off_t off = lseek(fd, 0, SEEK_END);
+
+  printf("offset: %ld\n", off);
+  
+  char buff2[32] = "Hello World!";
+
+  ssize_t wbit = write(fd, buff2, 13);
+  
+  printf("wbit: %ld\n", wbit);
+  
+
+  return 0;
+}
diff --git a/3/file/filesync.c b/3/file/filesync.c
new file mode 100644
index 0000000..f4a8dc8
--- /dev/null
+++ b/3/file/filesync.c
@@ -0,0 +1,51 @@
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdio.h>
+
+int readFile(){
+  
+  int fd2 = open("./test/fileat", O_RDONLY);
+
+  if(fd2 < 0){
+    printf("Error in opening file fileat\n");
+    return -1;
+  }
+
+  char buff2[1024];
+
+  ssize_t rbit = read(fd2, buff2, 1024);
+
+  if(rbit < 0){
+    printf("Error in reading file fileat\n");
+    return -1;
+  }
+  buff2[rbit] = 0;
+  printf("rbit: %ld %s", rbit, buff2);
+
+  close(fd2);
+  return 0;
+
+}
+
+int main(void){
+  int fd = open("./test/fileat", O_RDWR | O_APPEND);
+
+  char buff[] = "Helloworld";
+
+  ssize_t wbit = write(fd, buff, sizeof(buff));
+
+  if(wbit != sizeof(buff)){
+    printf("Error occur when wrote file fileat\n");
+    return -1;
+  }
+  
+  readFile();
+
+  fsync(fd);
+
+  readFile();
+  
+  close(fd);
+
+  return 0;
+}
diff --git a/3/file/openfile.c b/3/file/openfile.c
new file mode 100644
index 0000000..9e1f78d
--- /dev/null
+++ b/3/file/openfile.c
@@ -0,0 +1,35 @@
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdio.h>
+
+#define RWRR S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH
+
+int main(void) {
+  int fd = open("./test/file", O_RDONLY | O_CREAT, RWRR);
+  int fd2 = open("./test/", O_DIRECTORY | O_EXCL);
+
+  printf("%d\n", fd);
+  printf("%d\n", fd2);
+
+  int fd3 = openat(fd2, "./fileat", O_TRUNC | O_RDWR | O_CREAT | O_SYNC, RWRR);
+  
+  int fd4 = creat("./test/filecreat", S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+
+  off_t off = lseek(fd4, 8, SEEK_SET);
+  
+  off = lseek(fd4, -2, SEEK_CUR);
+
+  off = lseek(fd4, 1024, SEEK_CUR);
+
+  printf("%ld", off);
+
+  close(fd4);
+
+  close(fd3);
+
+  close(fd2);
+
+  close(fd);
+  
+  return 0;
+}
diff --git a/3/file/test/fileat b/3/file/test/fileat
new file mode 100644
index 0000000..78086f7
Binary files /dev/null and b/3/file/test/fileat differ
diff --git a/3/file/test/filecreat b/3/file/test/filecreat
new file mode 100644
index 0000000..e69de29