diff --git a/src/filesys/sysfile.c b/src/filesys/sysfile.c
index 998da9f..4ad2997 100644
--- a/src/filesys/sysfile.c
+++ b/src/filesys/sysfile.c
@@ -210,3 +210,20 @@ syscall_fstat(void)
         return SYS_FAIL_RC;
     return 0;
 }
+
+/** int32_t seek(int32_t fd, uint32_t offset); */
+int32_t
+syscall_seek(void)
+{
+    int32_t fd;
+    uint32_t offset;
+
+    if (!sysarg_get_int(0, &fd))
+        return SYS_FAIL_RC;
+    if (!sysarg_get_uint(1, &offset))
+        return SYS_FAIL_RC;
+
+    if (!filesys_seek(fd, offset))
+        return SYS_FAIL_RC;
+    return 0;
+}
diff --git a/src/filesys/sysfile.h b/src/filesys/sysfile.h
index 971c0aa..1e66be5 100644
--- a/src/filesys/sysfile.h
+++ b/src/filesys/sysfile.h
@@ -38,6 +38,7 @@ int32_t syscall_chdir();
 int32_t syscall_getcwd();
 int32_t syscall_exec();
 int32_t syscall_fstat();
+int32_t syscall_seek();
 
 
 #endif
diff --git a/src/filesys/vsfs.c b/src/filesys/vsfs.c
index 84ddc23..8bf66fd 100644
--- a/src/filesys/vsfs.c
+++ b/src/filesys/vsfs.c
@@ -679,6 +679,30 @@ filesys_fstat(int8_t fd, file_stat_t *stat)
 }
 
 
+/** Seek to absolute file offset. */
+bool
+filesys_seek(int8_t fd, size_t offset)
+{
+    file_t *file = _find_process_file(fd);
+    if (file == NULL) {
+        warn("seek: cannot find file for fd %d", fd);
+        return false;
+    }
+
+    inode_lock(file->inode);
+    size_t filesize = file->inode->d_inode.size;
+    inode_unlock(file->inode);
+
+    if (offset > filesize) {
+        warn("seek: offset %lu beyond filesize %lu", offset, filesize);
+        return false;
+    }
+
+    file->offset = offset;
+    return true;
+}
+
+
 /** Flush the in-memory modified bitmap block to disk. */
 bool
 inode_bitmap_update(uint32_t slot_no)
diff --git a/src/filesys/vsfs.h b/src/filesys/vsfs.h
index 3d2fb5e..1c38076 100644
--- a/src/filesys/vsfs.h
+++ b/src/filesys/vsfs.h
@@ -130,6 +130,8 @@ bool filesys_exec(char *path, char **argv);
 
 bool filesys_fstat(int8_t fd, file_stat_t *stat);
 
+bool filesys_seek(int8_t fd, size_t offset);
+
 bool inode_bitmap_update(uint32_t slot_no);
 bool data_bitmap_update(uint32_t slot_no);
 
diff --git a/src/interrupt/syscall.c b/src/interrupt/syscall.c
index 8b70385..91672a7 100644
--- a/src/interrupt/syscall.c
+++ b/src/interrupt/syscall.c
@@ -47,7 +47,8 @@ static syscall_t syscall_handlers[] = {
     [SYSCALL_CHDIR]     syscall_chdir,
     [SYSCALL_GETCWD]    syscall_getcwd,
     [SYSCALL_EXEC]      syscall_exec,
-    [SYSCALL_FSTAT]     syscall_fstat
+    [SYSCALL_FSTAT]     syscall_fstat,
+    [SYSCALL_SEEK]      syscall_seek
 };
 
 #define NUM_SYSCALLS ((int32_t) (sizeof(syscall_handlers) / sizeof(syscall_t)))
diff --git a/src/interrupt/syscall.h b/src/interrupt/syscall.h
index 27a7968..8414335 100644
--- a/src/interrupt/syscall.h
+++ b/src/interrupt/syscall.h
@@ -38,6 +38,7 @@
 #define SYSCALL_GETCWD  18
 #define SYSCALL_EXEC    19
 #define SYSCALL_FSTAT   20
+#define SYSCALL_SEEK    21
 
 
 /**
diff --git a/user/lib/syscall.h b/user/lib/syscall.h
index 893b25c..be9dd73 100644
--- a/user/lib/syscall.h
+++ b/user/lib/syscall.h
@@ -74,6 +74,7 @@ extern int32_t chdir(char *path);
 extern int32_t getcwd(char *buf, uint32_t limit);
 extern int32_t exec(char *path, char **argv);
 extern int32_t fstat(int32_t fd, file_stat_t *stat);
+extern int32_t seek(int32_t fd, uint32_t offset);
 
 
 #endif
diff --git a/user/lib/syscall.s b/user/lib/syscall.s
index fcbddf1..1ee6594 100644
--- a/user/lib/syscall.s
+++ b/user/lib/syscall.s
@@ -40,3 +40,4 @@ SYSCALL_LIBGEN  chdir,   SYSCALL_CHDIR
 SYSCALL_LIBGEN  getcwd,  SYSCALL_GETCWD
 SYSCALL_LIBGEN  exec,    SYSCALL_EXEC
 SYSCALL_LIBGEN  fstat,   SYSCALL_FSTAT
+SYSCALL_LIBGEN  seek,    SYSCALL_SEEK
diff --git a/user/lib/syslist.s b/user/lib/syslist.s
index d8319ee..968ff25 100644
--- a/user/lib/syslist.s
+++ b/user/lib/syslist.s
@@ -31,3 +31,4 @@ SYSCALL_CHDIR   = 17
 SYSCALL_GETCWD  = 18
 SYSCALL_EXEC    = 19
 SYSCALL_FSTAT   = 20
+SYSCALL_SEEK    = 21
diff --git a/user/put.c b/user/put.c
index 16feb55..86ba13e 100644
--- a/user/put.c
+++ b/user/put.c
@@ -44,7 +44,6 @@ _open_writable_file(char *path, bool overwrite)
 
     /** If not overwriting, seek to current file end. */
     if (!overwrite) {
-        assert(stat.size >= 0);
         int ret = seek(fd, stat.size);
         if (ret != 0) {
             warn("put: cannot seek to offset %lu", stat.size);
@@ -72,10 +71,11 @@ _file_put_str(char *path, char *str, size_t len, bool overwrite, bool newline)
     }
 
     /** If putting newline after string. */
-    if (newline)
+    if (newline) {
         bytes_written = write(fd, "\n", 1);
-    if (bytes_written != 1)
-        warn("put: newline written %lu != 1", bytes_written);
+        if (bytes_written != 1)
+            warn("put: newline written %lu != 1", bytes_written);
+    }
 
     close(fd);
 }
diff --git a/wiki b/wiki
index 716b0c6..668fd5e 160000
--- a/wiki
+++ b/wiki
@@ -1 +1 @@
-Subproject commit 716b0c601196aa8dff2d000c6b848476efb14ffe
+Subproject commit 668fd5e003e12cb470fa303cbb117dd66dd91e80