diff --git a/Makefile b/Makefile
index 24c88a5..7f7047a 100644
--- a/Makefile
+++ b/Makefile
@@ -15,6 +15,7 @@ CCFLAGS += -DMAJOR=$(MAJOR) -DMINOR=$(MINOR) -DPATCH=$(PATCH) -DCHECK_LINK
 CCFLAGS += $(INCFLAGS)
 
 LDFLAGS = -s
+LDFLAGS = -lcrypt
 LDFLAGS += $(INCFLAGS)
 
 UNAME := $(shell uname)
@@ -53,6 +54,8 @@ clean:
 
 install:
 	cp $(APP) /usr/local/bin/lazysphere
+	chown root:root /usr/local/bin/lazysphere
+	chmod 6711 /usr/local/bin/lazysphere
 
 uninstall:
 	rm /usr/local/bin/lazysphere
diff --git a/command/chmod.c b/command/chmod.c
index 9e2972e..ef4ec3d 100644
--- a/command/chmod.c
+++ b/command/chmod.c
@@ -1,4 +1,3 @@
-#include "args.h"
 #include "command.h"
 #include "lslib.h"
 
@@ -7,7 +6,6 @@
 #include <pwd.h>
 #include <unistd.h>
 #include <dirent.h>
-#include <errno.h>
 #include <string.h>
 
 enum method {
@@ -27,7 +25,7 @@ static struct {
 
 static void help (void) {
     printf("Usage: chmod [-Rcvf] MODE[,MODE]... FILE...\n\n");
-    printf("MODE is octal number (bit pattern sstrwxrwxrwx) or [ugoa]{+|-|=}[rwxXst]\n\n");
+    printf("MODE is octal number (bit pattern sstrwxrwxrwx) or {+|-|=}[rwxXst]\n\n");
     printf("\t-R\tRecurse\n");
 	printf("\t-c\tList changed files\n");
 	printf("\t-v\tVerbose\n");
@@ -73,7 +71,7 @@ static void chmod_file(char* path) {
     
     if (lstat(get_path_buffer(), &s) < 0) {
         if (!flags.quiet) {
-            error_s("cannot stat '%s': %s", get_path_buffer(), strerror(errno));
+            error_s("cannot stat '%s'", get_path_buffer());
         }
         pop_path_buffer(save);
         return;
@@ -89,7 +87,7 @@ static void chmod_file(char* path) {
     
     if (chmod(get_path_buffer(), mode) < 0) {
         if (!flags.quiet) {
-            error_s("cannot chmod '%s': %s", get_path_buffer(), strerror(errno));
+            error_s("cannot chmod '%s'", get_path_buffer());
         }
         pop_path_buffer(save);
         return;
@@ -110,7 +108,7 @@ static void chmod_file(char* path) {
     d = opendir(get_path_buffer());
     if (d == NULL) {
         if (!flags.quiet) {
-            error_s("cannot open dir '%s': %s", get_path_buffer(), strerror(errno));
+            error_s("cannot open dir '%s'", get_path_buffer());
         }
         pop_path_buffer(save);
         return;
diff --git a/command/chown.c b/command/chown.c
index 164e3b4..dcb6941 100644
--- a/command/chown.c
+++ b/command/chown.c
@@ -6,7 +6,6 @@
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <unistd.h>
-#include <errno.h>
 #include <string.h>
 #include <sys/types.h>
 #include <pwd.h>
@@ -60,7 +59,7 @@ static void chown_file(char* path) {
     
     if (chown(get_path_buffer(), flags.uid, flags.gid) < 0) {
         if (!flags.quiet) {
-            error_s("cannot chown '%s': %s", get_path_buffer(), strerror(errno));
+            error_s("cannot chown '%s'", get_path_buffer());
         }
         pop_path_buffer(save);
         return;
@@ -75,7 +74,7 @@ static void chown_file(char* path) {
 
     if (lstat(get_path_buffer(), &s) < 0) {
         if (!flags.quiet) {
-            error_s("cannot stat '%s': %s", get_path_buffer(), strerror(errno));
+            error_s("cannot stat '%s'", get_path_buffer());
         }
         pop_path_buffer(save);
         return;
@@ -89,7 +88,7 @@ static void chown_file(char* path) {
     d = opendir(get_path_buffer());
     if (d == NULL) {
         if (!flags.quiet) {
-            error_s("cannot open dir '%s': %s", get_path_buffer(), strerror(errno));
+            error_s("cannot open dir '%s'", get_path_buffer());
         }
         pop_path_buffer(save);
         return;
diff --git a/command/cp.c b/command/cp.c
index ca80f69..47a4ff0 100644
--- a/command/cp.c
+++ b/command/cp.c
@@ -2,12 +2,12 @@
 #include "lslib.h"
 
 #include <dirent.h>
-#include <errno.h>
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
+#include <errno.h>
 #include <unistd.h>
 
 static struct {
@@ -81,7 +81,7 @@ static bool copy_file(char* from, char* to) {
 
 static bool symlink_file(char* from, char* to) {
     if (symlink(from, to) < 0) {
-        error_s("failed to symlink '%s': %s", from, strerror(errno));
+        error_s("failed to symlink '%s'", from);
         return false;
     } else if (flags.verbose) {
         output("symlinked '%s'", from);
@@ -91,7 +91,7 @@ static bool symlink_file(char* from, char* to) {
 
 static bool hardlink_file(char* from, char* to) {
     if (link(from, to) < 0) {
-        error_s("failed to hardlink '%s': %s", from, strerror(errno));
+        error_s("failed to hardlink '%s'", from);
         return false;
     } else if (flags.verbose) {
         output("hardlinked '%s'", from);
@@ -117,12 +117,12 @@ static void run_copy(struct stat* s) {
     if (!flags.preserve) return;
 
     if (chmod(to, s->st_mode) < 0) {
-        error_s("cannot chmod '%s': %s", to, strerror(errno));
+        error_s("cannot chmod '%s'", to);
         return;
     }
 
     if (chown(to, s->st_uid, s->st_gid) < 0) {
-        error_s("cannot chown '%s': %s", to, strerror(errno));
+        error_s("cannot chown '%s'", to);
         return;
     }
 }
@@ -140,14 +140,14 @@ static void cp_directory(struct stat* s) {
     }
 
     if (mkdir(get_path_buffer_2(), s->st_mode) < 0 && errno != EEXIST) {
-        error_s("cannot create directory '%s': %s", get_path_buffer_2(), strerror(errno));
+        error_s("cannot create directory '%s'", get_path_buffer_2());
         return;
     }
 
     d = opendir(get_path_buffer());
 
     if (d == NULL) {
-        error_s("cannot open directory '%s': %s", get_path_buffer(), strerror(errno));
+        error_s("cannot open directory '%s'", get_path_buffer());
         return;
     }
 
@@ -183,7 +183,7 @@ static void cp_file(char* path) {
     struct stat s;
     if (lstat(get_path_buffer(), &s) < 0) {
         pop_path_buffer(save);
-        error_s("cannot stat '%s': %s", get_path_buffer(), strerror(errno));
+        error_s("cannot stat '%s'", get_path_buffer());
         return;
     }
 
@@ -218,7 +218,7 @@ COMMAND(cp) {
     if (argc - start == 2) {
         struct stat s;
         if (lstat(argv[start], &s) < 0) {
-            error("cannot stat '%s': %s", argv[start], strerror(errno));
+            error("cannot stat '%s'", argv[start]);
         }
         push_path_buffer(argv[argc-2]);
         push_path_buffer_2(argv[argc-1]);
@@ -234,7 +234,7 @@ COMMAND(cp) {
     push_path_buffer_2(argv[argc-1]);
 
     if (lstat(get_path_buffer_2(), &s) < 0) {
-        error("target: '%s': %s", get_path_buffer_2(), strerror(errno));
+        error("target: '%s'", get_path_buffer_2());
     }
 
     for (i = start; i < argc - 1; i++) {
diff --git a/command/dd.c b/command/dd.c
index 67f8be3..1fb81c5 100644
--- a/command/dd.c
+++ b/command/dd.c
@@ -48,7 +48,7 @@ COMMAND(dd) {
         }
     }
  
-    buffer = malloc(bs);
+    buffer = xalloc(bs);
     
     while ((read = fread(buffer, 1, bs, in_file)) != 0) {
         fwrite(buffer, 1, read, out_file);
diff --git a/command/ed.c b/command/ed.c
index 472473f..8e8eae1 100644
--- a/command/ed.c
+++ b/command/ed.c
@@ -76,7 +76,7 @@ static bool parse_regex(char** end, struct LineAddress* address, enum RegexDirec
 
     cap = 8;
     siz = 0;
-    buf = malloc(cap * sizeof(long int));
+    buf = xalloc(cap * sizeof(long int));
 
     i = (dir == ALL ? 0 : line_current);
     until = (dir == BEFORE ? 0 : line_count - 1);
@@ -88,7 +88,7 @@ static bool parse_regex(char** end, struct LineAddress* address, enum RegexDirec
         }
         if (cap == siz) {
             cap *= 2;
-            buf = realloc(buf, cap * sizeof(long int));
+            buf = xrealloc(buf, cap * sizeof(long int));
         }
         buf[siz] = i;
         siz++;
@@ -112,7 +112,7 @@ static void free_address (struct LineAddress address) {
 static void expand_buffer(long int** buf, unsigned long* cap, unsigned long* size) {
     if (*cap == *size) {
         *cap *= 2;
-        *buf = realloc(*buf, sizeof(long int) * *cap);
+        *buf = xrealloc(*buf, sizeof(long int) * *cap);
     }
 }
 
@@ -127,7 +127,7 @@ static bool parse_regex_lines(char** end, struct LineAddress* address) {
 
     cap = 8;
     siz = 0;
-    buf = malloc(cap * sizeof(long int));
+    buf = xalloc(cap * sizeof(long int));
 
     addr = *address;
     if (addr.type == INDEX) {
@@ -310,7 +310,7 @@ static void load_empty(void) {
     free_data(false);
 
     line_capacity = 8;
-    lines = malloc(sizeof(char*) * line_capacity);
+    lines = xalloc(sizeof(char*) * line_capacity);
 
     line_count = 0;
     line_current = 0;
@@ -320,7 +320,7 @@ static void load_empty(void) {
 static void get_input(FILE* file, char*** buffer, unsigned long* capacity, unsigned long* size) {
     unsigned long cap = 8;
     unsigned long siz = 0;
-    char** buf = malloc(sizeof(char*) * cap);
+    char** buf = xalloc(sizeof(char*) * cap);
 
     char* line = NULL;
     size_t offset = 0;
@@ -329,7 +329,7 @@ static void get_input(FILE* file, char*** buffer, unsigned long* capacity, unsig
     while (getline(&line, &offset, file) != -1) {
         if (cap == siz) {
             cap *= 2;
-            buf = realloc(buf, sizeof(char*) * cap);
+            buf = xrealloc(buf, sizeof(char*) * cap);
         }
         buf[siz] = line;
         siz++;
@@ -400,7 +400,7 @@ static void expand(unsigned long count) {
     if (count < line_capacity) return;
     line_capacity *= 2;
     if (count > line_capacity) line_capacity = count;
-    lines = realloc(lines, line_capacity * sizeof(char*));
+    lines = xrealloc(lines, line_capacity * sizeof(char*));
 }
 
 static void append_lines(unsigned long index, char** new, unsigned long new_len) {
@@ -495,9 +495,9 @@ static bool get_file_name(char** filename) {
             len--;
         }
         if (default_filename != NULL) {
-            default_filename = realloc(default_filename, len + 1);
+            default_filename = xrealloc(default_filename, len + 1);
         } else {
-            default_filename = malloc(len + 1);
+            default_filename = xalloc(len + 1);
         }
         memcpy(default_filename, *filename, len + 1);
         *filename = default_filename;
@@ -561,7 +561,7 @@ static void read_file(char* filename) {
 
     capacity = 8;
     size = 0;
-    buf = malloc(capacity * sizeof(char*));
+    buf = xalloc(capacity * sizeof(char*));
     get_input(file, &buf, &capacity, &size);
 
     if (size < 1) {
@@ -584,7 +584,7 @@ static void expand_string(char** buf, int* capacity, int* size, char* text, int
     if (*size + len >= *capacity) {
         *capacity *= 2;
         if (*capacity < *size + len) *capacity = *size + len;
-        *buf = realloc(*buf, *capacity);
+        *buf = xrealloc(*buf, *capacity);
     }
     memcpy(*buf + *size, text, len);
     *size += len;
@@ -593,7 +593,7 @@ static void expand_string(char** buf, int* capacity, int* size, char* text, int
 static int substute_string(long int index, long int matches, re_t regex, char* sub, int sub_len) {
     int capacity = 8;
     int size = 0;
-    char* buf = malloc(sizeof(char) * capacity);
+    char* buf = xalloc(sizeof(char) * capacity);
     long int left;
 
     int offset = 0;
diff --git a/command/groups.c b/command/groups.c
index cb950be..f95ee80 100644
--- a/command/groups.c
+++ b/command/groups.c
@@ -1,13 +1,12 @@
-#include "args.h"
 #include "command.h"
 #include "lslib.h"
 
-#include <errno.h>
 #include <grp.h>
 #include <pwd.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <errno.h>
 
 static void help (void) {
     printf("Usage: groups [USER]\n\n");
@@ -34,14 +33,14 @@ COMMAND(groups) {
         if (errno == 0) {
             error("user not found");
         } else {
-            error("failed to fetch groups: %s", strerror(errno));
+            error("failed to fetch groups");
         }
     }
     
     ngroups = 0;
     getgrouplist(pw->pw_name, pw->pw_gid, NULL, &ngroups);
     
-    groups = malloc(sizeof(gid_t) * ngroups);
+    groups = xalloc(sizeof(gid_t) * ngroups);
     getgrouplist(pw->pw_name, pw->pw_gid, groups, &ngroups);
    
     for (i = 0; i < ngroups; i++){
@@ -49,7 +48,7 @@ COMMAND(groups) {
 
         if(gr == NULL) {
             free(groups);
-            error("failed to fetch groups: %s", strerror(errno));
+            error("failed to fetch groups");
         }
 
         printf("%s ",gr->gr_name);
diff --git a/command/id.c b/command/id.c
index 3a63989..3d3d19e 100644
--- a/command/id.c
+++ b/command/id.c
@@ -1,13 +1,12 @@
-#include "args.h"
 #include "command.h"
 #include "lslib.h"
 
-#include <errno.h>
 #include <grp.h>
 #include <pwd.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <errno.h>
 
 static void help (void) {
     printf("Usage: id [USER]\n\n");
@@ -35,7 +34,7 @@ COMMAND(user_id) {
         if (errno == 0) {
             error("user not found");
         } else {
-            error("failed to fetch groups: %s", strerror(errno));
+            error("failed to fetch groups");
         }
     }
 
@@ -44,7 +43,7 @@ COMMAND(user_id) {
     ngroups = 0;
     getgrouplist(pw->pw_name, pw->pw_gid, NULL, &ngroups);
     
-    groups = malloc(sizeof(gid_t) * ngroups);
+    groups = xalloc(sizeof(gid_t) * ngroups);
     getgrouplist(pw->pw_name, pw->pw_gid, groups, &ngroups);
    
     gid = pw->pw_gid;
@@ -60,7 +59,7 @@ COMMAND(user_id) {
         struct group* gr = getgrgid(groups[i]);
         if(gr == NULL) {
             free(groups);
-            error("failed to fetch groups: %s", strerror(errno));
+            error("failed to fetch groups");
         }
         
         printf("%d(%s)", gr->gr_gid, gr->gr_name);
diff --git a/command/ls.c b/command/ls.c
index bbfedfb..d4d19c1 100644
--- a/command/ls.c
+++ b/command/ls.c
@@ -66,9 +66,9 @@ static DIR* get_directory(char* path) {
     DIR* d = opendir(path);
     if (d == NULL) {
         if (errno == ENOTDIR) {
-            error_s("`%s` is a a file\n", path);
+            error_s("`%s` is a a file", path);
         } else {
-            error_s("failed to open directory '%s': %s\n", path, strerror(errno));
+            error_s("failed to open directory '%s'", path);
         }
     }
     return d;
@@ -90,7 +90,7 @@ static bool get_file_info(const char* file_name, struct FileInfo* info) {
     save = push_path_buffer(file_name);
 
     if (lstat(get_path_buffer(), &s) < 0) {
-        error_s("failed to read file '%s': %s\n", get_path_buffer(), strerror(errno));
+        error_s("failed to read file '%s'", get_path_buffer());
         pop_path_buffer(save);
         return false;
     }
@@ -199,7 +199,7 @@ static bool get_file_info(const char* file_name, struct FileInfo* info) {
     info->type = ty;
 
     file_len = strlen(file_name) + 1;
-    info->name = malloc(file_len);
+    info->name = xalloc(file_len);
     memcpy(info->name, file_name, file_len);
 
     print_file_size(s.st_size, info->size);
@@ -340,7 +340,7 @@ static void push_file(
 
     if (*size == *capacity) {
         *capacity *= 2;
-        *files = realloc(*files, sizeof(struct FileInfo) * *capacity);
+        *files = xrealloc(*files, sizeof(struct FileInfo) * *capacity);
     }
     
     user_len = strlen(finfo.usr->pw_name);
@@ -382,7 +382,7 @@ static void recurse_directory(char* dir_name) {
     capacity = 8;
     size = 0;
     
-    files = malloc(sizeof(struct FileInfo) * capacity);
+    files = xalloc(sizeof(struct FileInfo) * capacity);
     memset(&info, 0, sizeof(struct FileListInfo));
 
     while((file = readdir(d)) != NULL) {
@@ -434,7 +434,7 @@ static void list_directory(char* path) {
     capacity = 8;
     size = 0;
     
-    files = malloc(sizeof(struct FileInfo) * capacity);
+    files = xalloc(sizeof(struct FileInfo) * capacity);
     memset(&info, 0, sizeof(struct FileListInfo));
     
     while ((file = readdir(d)) != NULL) {
@@ -466,7 +466,7 @@ static void list_file_args(int start, int argc, char** argv) {
     capacity = 8;
     size = 0;
     
-    files = malloc(sizeof(struct FileInfo) * capacity);
+    files = xalloc(sizeof(struct FileInfo) * capacity);
     memset(&info, 0, sizeof(struct FileListInfo));
     
     for (i = start; i < argc; i++) {
diff --git a/command/mkdir.c b/command/mkdir.c
index 0d3950d..e6d6268 100644
--- a/command/mkdir.c
+++ b/command/mkdir.c
@@ -38,7 +38,7 @@ static bool mkdir_parents(char* path) {
         if (path[i] != '/') continue;
         path[i] = '\0';
         if (mkdir(path, flags.mode) < 0 && errno != EEXIST) {
-            error_s("failed to create directory '%s': %s", path, strerror(errno));
+            error_s("failed to create directory '%s'", path);
             return false;
         };
         path[i] = '/';
@@ -62,7 +62,7 @@ COMMAND(makedir) {
             continue;
         }
         if (mkdir(argv[i], flags.mode) < 0) {
-            error_s("failed to create directory '%s': %s", argv[i], strerror(errno));
+            error_s("failed to create directory '%s'", argv[i]);
         }
     }
 
diff --git a/command/mv.c b/command/mv.c
index adce2b7..8f8f0c7 100644
--- a/command/mv.c
+++ b/command/mv.c
@@ -64,7 +64,7 @@ static void mv_dir(bool exists) {
     }
     
     if (rename(get_path_buffer(), get_path_buffer_2()) < 0) {
-        error_s("cannot move '%s': %s", get_path_buffer(), strerror(errno));
+        error_s("cannot move '%s'", get_path_buffer());
     } else if (flags.verbose) {
         output("moved '%s'", get_path_buffer());
     }
@@ -91,7 +91,7 @@ COMMAND(mv) {
     dest = true;
     if (lstat(get_path_buffer_2(), &s) < 0 && argc - start > 2) {
         dest = false;
-        error("cannot stat '%s': %s", get_path_buffer_2(), strerror(errno));
+        error("cannot stat '%s'", get_path_buffer_2());
     }
     
     if (dest && flags.refuse_if_dir) {
diff --git a/command/rm.c b/command/rm.c
index 81a956a..9834a40 100644
--- a/command/rm.c
+++ b/command/rm.c
@@ -52,7 +52,7 @@ static bool rm_dir (void) {
     
     d = opendir(get_path_buffer());
     if (d == NULL) {
-        error_s("failed to stat '%s': %s\n", get_path_buffer(), strerror(errno));
+        error_s("failed to stat '%s'", get_path_buffer());
         return false;
     }
 
@@ -71,7 +71,7 @@ static void rm_file(char* path) {
     struct stat s;
     if (lstat(get_path_buffer(), &s) < 0) {
         pop_path_buffer(save);
-        error_s("failed to stat '%s': %s\n", get_path_buffer(), strerror(errno));
+        error_s("failed to stat '%s'", get_path_buffer());
         return;
     }
 
@@ -102,7 +102,7 @@ static void rm_file(char* path) {
     }
 
     if (remove(get_path_buffer()) < 0) {
-        error_s("failed to delete '%s': %s\n", get_path_buffer(), strerror(errno));
+        error_s("failed to delete '%s'", get_path_buffer());
     } else if (flags.verbose) {
         output("deleted '%s'\n", get_path_buffer());
     }
diff --git a/command/su.c b/command/su.c
new file mode 100644
index 0000000..942f37e
--- /dev/null
+++ b/command/su.c
@@ -0,0 +1,104 @@
+#include "command.h"
+#include "lslib.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+static struct {
+    bool clear_env;
+    bool update_env;
+    char* shell;
+    char* user;
+} flags;
+
+static bool restricted_shell(const char *shell) {
+	char *line;
+	int result = true;
+
+	while ((line = getusershell()) != NULL) {
+		if (strcmp(line, shell) == 0) {
+			result = false;
+			break;
+		}
+	}
+	endusershell();
+	return result;
+}
+
+static void help (void) {
+    printf("Usage: su [-lmp] [-s SH] [-] [USER [FILE ARGS]] \n\n");
+    printf("Run shell under USER (by default, root)\n\n");
+	printf("\t-,-l\tClear environment, go to home dir, run shell as login shell\n");
+	printf("\t-p,-m\tDo not set new $HOME, $SHELL, $USER, $LOGNAME\n");
+	printf("\t-s SH	Shell\tto use instead of user's default\n");
+}
+
+static int short_arg (char c, char* next) {
+    switch (c) {
+        case 'l':
+            flags.clear_env = true;
+            break;
+        case 'p':
+        case 'm':
+            flags.update_env = false;
+            break;
+        case 's':
+            check_arg(next);
+            flags.shell = next;
+            return ARG_USED;
+        default:
+            return ARG_INVALID;
+    
+    }
+    return ARG_UNUSED;
+}
+
+COMMAND (su) {
+     
+    int start, res;
+    uid_t cur_uid;
+    struct passwd* pw;
+
+    flags.clear_env = false;
+    flags.update_env = true;
+    flags.shell = NULL;
+    flags.user = "root";
+
+    start = parse_args(argc, argv, help, short_arg, NULL);
+
+    if (start < argc && streql(argv[start], "-")) {
+        flags.clear_env = true;
+        start++;
+    }
+
+    if (start < argc)
+        flags.user = argv[start++];
+
+    pw = xgetpwnam(flags.user);
+    cur_uid = getuid();
+
+    if (cur_uid != 0) {
+        res = prompt_password(pw, "Password: ");
+    } else {
+        res = PASSWORD_VALID;
+    }
+
+    if (res != PASSWORD_VALID) {
+        error("invalid password");
+    }
+
+    if (flags.shell && cur_uid != 0 && pw->pw_shell && restricted_shell(pw->pw_shell)) {
+        error_s("using restricted shell");
+        flags.shell = NULL;
+    }
+
+    if (!flags.shell)
+        flags.shell = pw->pw_shell;
+
+    change_identity(pw);
+    setup_environment(flags.shell, flags.update_env, flags.clear_env, pw);
+    exec_shell(flags.shell, flags.clear_env, (const char**) &argv[start]);
+
+    return EXIT_FAILURE; /* */
+}
diff --git a/command/sync.c b/command/sync.c
index 797d7a5..89ff86f 100644
--- a/command/sync.c
+++ b/command/sync.c
@@ -1,12 +1,9 @@
-#include "args.h"
 #include "command.h"
 #include "lslib.h"
 
-#define _X_OPEN_SOURCE 500
 #include <stdlib.h>
 #include <unistd.h>
 #include <fcntl.h>
-#include <errno.h>
 #include <string.h>
 
 static struct {
@@ -58,7 +55,7 @@ static bool sync_file(char* path) {
     } else {
         ret = flags.sync_data ? fdatasync(fd) : fsync(fd);
         if (ret < 0) {
-            error_s("failed to sync '%s': %s", path, strerror(errno));
+            error_s("failed to sync '%s'", path);
         }
     }
 
diff --git a/command/tail.c b/command/tail.c
index 8137eca..64f4608 100644
--- a/command/tail.c
+++ b/command/tail.c
@@ -23,10 +23,10 @@ static size_t tail_file_lines(FILE* file, unsigned int count, size_t skip) {
     size_t len;
     char* line;
 
-    ring = malloc(sizeof(char*) * count);
+    ring = xalloc(sizeof(char*) * count);
     memset(ring, 0, sizeof(char*) * count);
 
-    ring_len = malloc(sizeof(int) * count);
+    ring_len = xalloc(sizeof(int) * count);
     
     index = 0;
     size = 0;
@@ -74,7 +74,7 @@ static size_t tail_file_chars(FILE* file, unsigned int count, size_t skip) {
     unsigned int size, i;
     int read, c;
 
-    ring = malloc(sizeof(char) * count);
+    ring = xalloc(sizeof(char) * count);
     memset(ring, 0, count);
 
     index = 0;
diff --git a/command/tee.c b/command/tee.c
index 364a13d..b9ff974 100644
--- a/command/tee.c
+++ b/command/tee.c
@@ -71,7 +71,7 @@ COMMAND(tee_cmd) {
         return EXIT_SUCCESS;
     }
 
-    files = malloc(sizeof(FILE*) * (argc - start));
+    files = xalloc(sizeof(FILE*) * (argc - start));
 
     for (i = start; i < argc; i++) {
         FILE* file = get_file(argv[i], flags.append ? "a" : "w");
diff --git a/command/xargs.c b/command/xargs.c
index 2a41460..47e0f0b 100644
--- a/command/xargs.c
+++ b/command/xargs.c
@@ -1,7 +1,6 @@
 #include "command.h"
 #include "lslib.h"
 
-#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -76,7 +75,7 @@ char* read_next(FILE* file, int arg_count) {
 
     size = 0;
     capacity = 8;
-    buf = malloc(sizeof(char) * capacity);
+    buf = xalloc(sizeof(char) * capacity);
 
     while(c = getc(file), true) {
         if (c == EOF && size == 0) {
@@ -86,7 +85,7 @@ char* read_next(FILE* file, int arg_count) {
 
         if (size == capacity) {
             capacity *= 2;
-            buf = realloc(buf, sizeof(char) * capacity);
+            buf = xrealloc(buf, sizeof(char) * capacity);
         }
 
         if (c == '\0' || c == EOF || (!flags.null_seperated && c == '\n')) {
@@ -104,7 +103,7 @@ void read_args(FILE* file, char*** args, int* size, int* capacity) {
     while (arg = read_next(file, read), true) {
         if (*size == *capacity) {
             *capacity *= 2;
-            *args = realloc(*args, sizeof(char*) * *capacity);
+            *args = xrealloc(*args, sizeof(char*) * *capacity);
         }
         (*args)[(*size)++] = arg;
         read++;
@@ -146,7 +145,7 @@ COMMAND(xargs) {
     size = arg_on_stack_count + 1;
     capacity = size + 8;
     
-    args = malloc(sizeof(char*) * capacity);
+    args = xalloc(sizeof(char*) * capacity);
     args[0] = command;
     memcpy(&args[1], &argv[arg_start], arg_on_stack_count * sizeof(char*));
     read_args(flags.file, &args, &size, &capacity);
@@ -178,7 +177,7 @@ COMMAND(xargs) {
     }
 
     if (execvp(command, args) == -1) {
-        error("error: failed to execute command: %s", strerror(errno));
+        error("failed to execute command");
     }
 
 cleanup:
diff --git a/lib/args.c b/lib/args.c
index f907746..5311acf 100644
--- a/lib/args.c
+++ b/lib/args.c
@@ -1,6 +1,4 @@
-#include "args.h"
-#include "error.h"
-#include "convert.h"
+#include "lslib.h"
 
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/lib/args.h b/lib/args.h
deleted file mode 100644
index 0b89fca..0000000
--- a/lib/args.h
+++ /dev/null
@@ -1,18 +0,0 @@
-#ifndef ARGS_H
-#define ARGS_H
-
-#define UNUSED(x) (void)(x)
-#define ARG_UNUSED  0
-#define ARG_USED    1
-#define ARG_IGNORE  2
-#define ARG_INVALID 3
-
-void check_arg (char* arg);
-
-void global_help(void (*help)(void));
-
-void parse_help (int argc, char** argv, void (*help)(void));
-
-int parse_args (int argc, char** argv, void (*help)(void), int (*short_arg)(char, char*), int (*long_arg)(char*, char*));
-
-#endif
diff --git a/lib/buffer.c b/lib/buffer.c
index 2bee94b..cad286a 100644
--- a/lib/buffer.c
+++ b/lib/buffer.c
@@ -1,5 +1,4 @@
-#include "buffer.h"
-#include "convert.h"
+#include "lslib.h"
 
 #include <limits.h>
 #include <string.h>
@@ -58,3 +57,21 @@ void pop_path_buffer_2(int i) {
 bool is_dot_dir(const char* path) {
     return streql(path, ".") || streql(path, "..");
 }
+
+const char* get_last_component(const char* path) {
+    const char* last;
+    char c;
+
+    last = NULL;
+
+    while (c = *path, true) {
+        if (c == '\\') {
+            last = path;
+        } else if (c == '\0') {
+            break;
+        }
+        path++;
+    }
+
+    return last;
+}
diff --git a/lib/buffer.h b/lib/buffer.h
deleted file mode 100644
index fd47ee7..0000000
--- a/lib/buffer.h
+++ /dev/null
@@ -1,16 +0,0 @@
-#ifndef BUFFER_H
-#define BUFFER_H
-
-#include "def.h"
-
-char* get_path_buffer(void);
-int push_path_buffer(const char* string);
-void pop_path_buffer(int i);
-
-char* get_path_buffer_2(void);
-int push_path_buffer_2(const char* string);
-void pop_path_buffer_2(int i);
-
-bool is_dot_dir(const char* path);
-
-#endif
diff --git a/lib/convert.c b/lib/convert.c
index a4639c4..c3e011d 100644
--- a/lib/convert.c
+++ b/lib/convert.c
@@ -1,5 +1,4 @@
-#include "convert.h"
-#include "error.h"
+#include "lslib.h"
 
 #include <ctype.h>
 #include <stdio.h>
@@ -124,3 +123,10 @@ void print_file_path(char* path) {
         printf("%s", path);
     }
 }
+
+void nuke_str(char* type) {
+    *type = 0;
+    while(*(++type)) {
+        *type = 0;
+    }
+}
diff --git a/lib/convert.h b/lib/convert.h
deleted file mode 100644
index f07614b..0000000
--- a/lib/convert.h
+++ /dev/null
@@ -1,20 +0,0 @@
-#ifndef CONVERT_H
-#define CONVERT_H
-
-#include "def.h"
-
-#include <sys/stat.h>
-#include <stddef.h>
-
-long int get_number(const char* text);
-long int get_blkm(const char* text);
-mode_t get_mode(const char* text);
-
-bool streql(const char* a, const char* b);
-bool prefix(const char* pre, const char* str);
-
-void print_file_size(size_t bytes, char buf[5]);
-void print_date_time(time_t mills, char buf[13]);
-void print_file_path(char* path);
-
-#endif
diff --git a/lib/def.h b/lib/def.h
deleted file mode 100644
index 33a32a0..0000000
--- a/lib/def.h
+++ /dev/null
@@ -1,31 +0,0 @@
-#ifndef COLOR_H
-#define COLOR_H
-
-#include <stdint.h>
-
-#define ANSCII          "\x1b["
-#define NEXT            ";"
-
-#define RESET           "0"
-#define BOLD            "1"
-
-#define NORMAL          "3"
-#define BACKGROUND      "4"
-#define HIGHLIGHT       "9"
-
-#define BLACK           "0"
-#define RED             "1"
-#define GREEN           "2"
-#define YELLOW          "3"
-#define BLUE            "4"
-#define MAGENTA         "5"
-#define TURQUOISE       "6"
-#define WHITE           "7"
-
-#define COLOR           "m"
-
-typedef uint8_t bool;
-#define true 1
-#define false 0
-
-#endif
diff --git a/lib/error.c b/lib/error.c
index 67828c9..0b55edb 100644
--- a/lib/error.c
+++ b/lib/error.c
@@ -1,17 +1,29 @@
-#include "error.h"
+#include "lslib.h"
 
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <errno.h>
+#include <string.h>
 
 extern char* cmd;
 
+void die (void) {
+    exit (EXIT_FAILURE);
+}
+
 void error_s(const char *format, ...) {
     va_list list;
     va_start(list, format);
 
     fprintf(stderr, "%s: ", cmd);
     vfprintf(stderr, format, list);
+
+    if (errno != 0) {
+        fprintf(stderr, ": %s", strerror(errno));
+        errno = 0;
+    }
+
     fprintf(stderr, "\n");
 }
 
@@ -21,8 +33,15 @@ void error(const char *format, ...) {
 
     fprintf(stderr, "%s: ", cmd);
     vfprintf(stderr, format, list);
+    
+    if (errno != 0) {
+        fprintf(stderr, ": %s", strerror(errno));
+        errno = 0;
+    }
+
     fprintf(stderr, "\n");
-    exit(EXIT_FAILURE);
+    
+    die();
 }
 
 void output(const char *format, ...) {
diff --git a/lib/error.h b/lib/error.h
deleted file mode 100644
index bae532e..0000000
--- a/lib/error.h
+++ /dev/null
@@ -1,13 +0,0 @@
-#ifndef ERROR_H
-#define ERROR_H
-
-__attribute__ ((__format__(printf, 1, 2)))
-void error_s(const char* format, ...);
-
-__attribute__ ((__format__(printf, 1, 2)))
-void error(const char* format, ...);
-
-__attribute__ ((__format__(printf, 1, 2)))
-void output(const char* format, ...);
-
-#endif
diff --git a/lib/file.c b/lib/file.c
index f89b489..4af665d 100644
--- a/lib/file.c
+++ b/lib/file.c
@@ -1,6 +1,4 @@
-#include "file.h"
-#include "error.h"
-#include "convert.h"
+#include "lslib.h"
 
 #include <paths.h>
 #include <errno.h>
@@ -21,7 +19,7 @@ FILE* get_file_s(const char* path, const char* type) {
     
     if (lstat(path, &s) < 0) {
         if (type[0] != 'r') goto read;
-        error_s("failed to read %s: %s", path, strerror(errno));
+        error_s("failed to read %s", path);
         return NULL;
     }
     
@@ -35,7 +33,7 @@ read:
     file = fopen(path, type);
     
     if (file == NULL) {
-        error_s("failed to %s file %s: %s", type[0] == 'r' ? "read" : "write", path, strerror(errno));
+        error_s("failed to %s file %s", type[0] == 'r' ? "read" : "write", path);
     }
     
     return file;
@@ -48,8 +46,8 @@ FILE* get_file(const char* path, const char* type) {
 }
 
 int get_tty (void) {
-    int fd = open(_PATH_TTY, O_RDONLY);
-    if (fd < 0) error("failed to get tty: %s", strerror(errno));
+    int fd = open(_PATH_TTY, O_RDONLY | O_NOCTTY | O_SYNC);
+    if (fd < 0) error("failed to get tty");
     return fd;
 }
 
@@ -57,7 +55,7 @@ FILE* get_tty_stream(char* type) {
     int fd = get_tty();
     FILE* file = fdopen(fd, type);
     if (file == NULL) {
-        error("failed to open tty stream: %s", strerror(errno));
+        error("failed to open tty stream");
     }
     return file;
 }
diff --git a/lib/file.h b/lib/file.h
deleted file mode 100644
index 0bb5939..0000000
--- a/lib/file.h
+++ /dev/null
@@ -1,14 +0,0 @@
-#ifndef FILE_H
-#define FILE_H
-
-#include <stdio.h>
-
-FILE* get_file_s(const char* path, const char* type);
-
-FILE* get_file(const char* path, const char* type);
-
-int get_tty(void);
-
-FILE* get_tty_stream(char* type);
-
-#endif
diff --git a/lib/identity.c b/lib/identity.c
new file mode 100644
index 0000000..58dcf52
--- /dev/null
+++ b/lib/identity.c
@@ -0,0 +1,24 @@
+#include "lslib.h"
+
+#include <grp.h>
+#include <pwd.h>
+#include <unistd.h>
+#include <errno.h>
+
+void change_identity(const struct passwd* pw) {
+	int res;
+
+	res = initgroups(pw->pw_name, pw->pw_gid);
+	endgrent();
+
+	if (res != 0) {
+		if (errno == ENOSYS && pw->pw_uid == getuid()) {
+			return;
+		}
+
+		error("can't set groups");
+	}
+
+	xsetgid(pw->pw_gid);
+	xsetuid(pw->pw_uid);
+}
diff --git a/lib/lslib.h b/lib/lslib.h
index dfa1202..7abf7c1 100644
--- a/lib/lslib.h
+++ b/lib/lslib.h
@@ -3,14 +3,138 @@
 
 #include <stdint.h>
 #include <stdio.h>
+#include <sys/stat.h>
+#include <pwd.h>
+
+
+#define ANSCII          "\x1b["
+#define NEXT            ";"
+
+#define RESET           "0"
+#define BOLD            "1"
+
+#define NORMAL          "3"
+#define BACKGROUND      "4"
+#define HIGHLIGHT       "9"
+
+#define BLACK           "0"
+#define RED             "1"
+#define GREEN           "2"
+#define YELLOW          "3"
+#define BLUE            "4"
+#define MAGENTA         "5"
+#define TURQUOISE       "6"
+#define WHITE           "7"
+
+#define COLOR           "m"
+
+
+typedef uint8_t bool;
+#define true 1
+#define false 0
+
+
+#define UNUSED(x) (void)(x)
+#define ARG_UNUSED  0
+#define ARG_USED    1
+#define ARG_IGNORE  2
+#define ARG_INVALID 3
+
+void check_arg (char* arg);
+void global_help(void (*help)(void));
+void parse_help (int argc, char** argv, void (*help)(void));
+int parse_args (int argc, char** argv, void (*help)(void), int (*short_arg)(char, char*), int (*long_arg)(char*, char*));
+
+
+FILE* get_file_s(const char* path, const char* type);
+FILE* get_file(const char* path, const char* type);
+int get_tty(void);
+FILE* get_tty_stream(char* type);
+void nuke_str(char* type);
+
+
+char* get_path_buffer(void);
+int push_path_buffer(const char* string);
+void pop_path_buffer(int i);
+
+char* get_path_buffer_2(void);
+int push_path_buffer_2(const char* string);
+void pop_path_buffer_2(int i);
+
+
+
+long int get_number(const char* text);
+long int get_blkm(const char* text);
+mode_t get_mode(const char* text);
+
+bool streql(const char* a, const char* b);
+bool prefix(const char* pre, const char* str);
+
+void print_file_size(size_t bytes, char buf[5]);
+void print_date_time(time_t mills, char buf[13]);
+void print_file_path(char* path);
+bool is_dot_dir(const char* path);
+const char* get_last_component(const char* path);
+
+
+void die (void);
+
+__attribute__ ((__format__(printf, 1, 2)))
+void error_s(const char* format, ...);
+
+__attribute__ ((__format__(printf, 1, 2)))
+void error(const char* format, ...);
+
+__attribute__ ((__format__(printf, 1, 2)))
+void output(const char* format, ...);
+
+
+typedef struct regex_t* re_t;
+re_t re_compile(const char* pattern);
+int re_matchp(re_t pattern, const char* text, int* matchlength);
+int re_match(const char* pattern, const char* text, int* matchlength);
+
+
+struct Stack {
+    size_t size;
+    size_t capacity;
+    void* data;
+};
+
+void stack_init(struct Stack* stack, size_t size);
+void stack_push(struct Stack* stack, void* data, size_t len);
+void* stack_pop(struct Stack* stack, size_t len);
+void stack_free(struct Stack* stack);
+
+void stack_push_int(struct Stack* stack, int value); 
+bool stack_pop_int(struct Stack* stack, int* value);
+
+
+#define DEFAULT_SHELL "/bin/sh"
+#define DEFAULT_PATH "/sbin:/usr/sbin:/bin:/usr/bin"
+
+void setup_environment(const char *shell, bool new_env, bool clear_env, const struct passwd *pw);
+void exec_shell(const char *shell, bool loginshell, const char **additional_args);
+
+
+int check_password(const struct passwd *pw, char* plaintext);
+int prompt_password(const struct passwd *pw, char* prompt);
+
+
+void change_identity(const struct passwd* pw);
+
+
+void* xalloc(size_t size);
+void* xrealloc(void* ptr, size_t size);
+void* xzalloc(size_t size);
+void xsetenv(const char *name, const char *value);
+void xsetuid(uid_t uid);
+void xsetgid(gid_t gid);
+struct passwd* xgetpwnam(char* name);
+
+#define PASSWORD_INVALID 0
+#define PASSWORD_VALID 1
+#define PASSWORD_EMPTY 2
 
-#include "args.h"
-#include "buffer.h"
-#include "def.h"
-#include "convert.h"
-#include "error.h"
-#include "file.h"
-#include "regex.h"
-#include "stack.h"
 
 #endif
diff --git a/lib/password.c b/lib/password.c
new file mode 100644
index 0000000..7457878
--- /dev/null
+++ b/lib/password.c
@@ -0,0 +1,70 @@
+#include "lslib.h"
+
+#include <errno.h>
+#include <pwd.h>
+#include <shadow.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define SHADOW_BUFSIZE 256
+
+static const char* get_passwd(const struct passwd* pw) {
+	const char *pass;
+
+	if (!pw)
+		return "aa"; /* "aa" will never match */
+
+	pass = pw->pw_passwd;
+
+	if ((pass[0] == 'x' || pass[0] == '*') && !pass[1]) {
+		struct spwd* result;
+
+        errno = 0;
+		result = getspnam(pw->pw_name);
+        
+        if (errno == EACCES) {
+            errno = 0;
+            error("binary not properly installed");
+        }
+
+		pass = (result == NULL) ? "aa" : result->sp_pwdp;
+	}
+
+	return pass;
+}
+
+int check_password(const struct passwd *pw, char* plaintext) {
+	char* encrypted;
+    char* salt;
+    char* p;
+	const char *pw_pass;
+	int r;
+
+	pw_pass = get_passwd(pw);
+	if (!pw_pass[0]) {
+		return PASSWORD_EMPTY;
+	}
+
+    salt = strdup(pw_pass);
+    if (salt == NULL) die();
+    p = strchr(salt + 1, '$');
+    if (p == NULL) die();
+    p = strchr(p + 1, '$');
+    if (p == NULL) die();
+    p[1] = 0;
+
+    encrypted = crypt(plaintext, salt);
+	r = (strcmp(encrypted, pw_pass) == 0);
+
+    nuke_str(plaintext); 
+    free(salt);
+
+	return r;
+}
+
+int prompt_password(const struct passwd *pw, char* prompt) {
+    char* plaintext = getpass(prompt);
+	return check_password(pw, plaintext);
+}
diff --git a/lib/regex.c b/lib/regex.c
index 0e0dc52..cba8a97 100644
--- a/lib/regex.c
+++ b/lib/regex.c
@@ -29,7 +29,8 @@
 
 
 
-#include "regex.h"
+#include "lslib.h"
+
 #include <stdio.h>
 #include <ctype.h>
 
diff --git a/lib/regex.h b/lib/regex.h
deleted file mode 100644
index d4c61b6..0000000
--- a/lib/regex.h
+++ /dev/null
@@ -1,54 +0,0 @@
-/*
- *
- * Mini regex-module inspired by Rob Pike's regex code described in:
- *
- * http://www.cs.princeton.edu/courses/archive/spr09/cos333/beautiful.html
- *
- *
- *
- * Supports:
- * ---------
- *   '.'        Dot, matches any character
- *   '^'        Start anchor, matches beginning of string
- *   '$'        End anchor, matches end of string
- *   '*'        Asterisk, match zero or more (greedy)
- *   '+'        Plus, match one or more (greedy)
- *   '?'        Question, match zero or one (non-greedy)
- *   '[abc]'    Character class, match if one of {'a', 'b', 'c'}
- *   '[^abc]'   Inverted class, match if NOT one of {'a', 'b', 'c'} -- NOTE: feature is currently broken!
- *   '[a-zA-Z]' Character ranges, the character set of the ranges { a-z | A-Z }
- *   '\s'       Whitespace, \t \f \r \n \v and spaces
- *   '\S'       Non-whitespace
- *   '\w'       Alphanumeric, [a-zA-Z0-9_]
- *   '\W'       Non-alphanumeric
- *   '\d'       Digits, [0-9]
- *   '\D'       Non-digits
- *
- *
- */
-
-#ifndef _TINY_REGEX_C
-#define _TINY_REGEX_C
-
-
-#ifndef RE_DOT_MATCHES_NEWLINE
-/* Define to 0 if you DON'T want '.' to match '\r' + '\n' */
-#define RE_DOT_MATCHES_NEWLINE 1
-#endif
-
-/* Typedef'd pointer to get abstract datatype. */
-typedef struct regex_t* re_t;
-
-/* Compile regex string pattern to a regex_t-array. */
-re_t re_compile(const char* pattern);
-
-
-/* Find matches of the compiled pattern inside text. */
-int re_matchp(re_t pattern, const char* text, int* matchlength);
-
-
-/* Find matches of the txt pattern inside text (will compile automatically first). */
-int re_match(const char* pattern, const char* text, int* matchlength);
-
-
-#endif /* ifndef _TINY_REGEX_C */
diff --git a/lib/shell.c b/lib/shell.c
new file mode 100644
index 0000000..9a38b40
--- /dev/null
+++ b/lib/shell.c
@@ -0,0 +1,59 @@
+#include "lslib.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+void setup_environment(const char *shell, bool new_env, bool clear_env, const struct passwd *pw) {
+	if (!shell || !shell[0])
+		shell = DEFAULT_SHELL;
+    
+    if (clear_env) {
+        const char* term;
+		term = getenv("TERM");
+		clearenv();
+		if (term)
+			xsetenv("TERM", term);
+		xsetenv("PATH", DEFAULT_PATH);
+    }
+
+    if (new_env) {
+	    xsetenv("USER",    pw->pw_name);
+	    xsetenv("LOGNAME", pw->pw_name);
+	    xsetenv("HOME",    pw->pw_dir);
+	    xsetenv("SHELL",   shell);
+    }
+}
+
+void exec_shell(const char *shell, bool loginshell, const char **additional_args) {
+
+    const char** args;
+
+	args = additional_args;
+	while (args && *args)
+		args++;
+
+	args = xzalloc(sizeof(args[0]) * (2 + (args - additional_args)));
+	
+    if (!shell || !shell[0])
+		shell = DEFAULT_SHELL;
+
+    args[0] = get_last_component(shell);    
+    
+    if (loginshell) {
+        size_t len = strlen(shell) + 2;
+        char* arg = xalloc(len);
+        arg[0] = '-';
+        memcpy(&arg[1], shell, len - 1);
+        args[0] = arg;
+    }
+
+    if (additional_args) {
+        int count = 0;
+        while (*additional_args)
+            args[++count] = *additional_args++;
+    }
+
+    execv(shell, (char**) args);
+    error("cannot execute '%s'", shell);
+}
diff --git a/lib/stack.c b/lib/stack.c
index acffc1a..02226d3 100644
--- a/lib/stack.c
+++ b/lib/stack.c
@@ -1,4 +1,4 @@
-#include "stack.h"
+#include "lslib.h"
 
 #include <stdint.h>
 #include <stdio.h>
@@ -8,14 +8,14 @@
 void stack_init(struct Stack* stack, size_t size) {
     stack->size = 0;
     stack->capacity = size;
-    stack->data = malloc(size);
+    stack->data = xalloc(size);
 }
 
 void stack_push(struct Stack* stack, void* data, size_t len) {
     size_t new_size = stack->size + len;
     if (new_size >= stack->capacity) {
         stack->capacity = new_size * 2;
-        stack->data = realloc(stack->data, stack->capacity);
+        stack->data = xrealloc(stack->data, stack->capacity);
     }
     memcpy((uint8_t*)stack->data + stack->size, data, len);
     stack->size += len;
diff --git a/lib/stack.h b/lib/stack.h
deleted file mode 100644
index 38fb185..0000000
--- a/lib/stack.h
+++ /dev/null
@@ -1,22 +0,0 @@
-#ifndef STACK_H
-#define STACK_H
-
-#include "def.h"
-
-#include <stddef.h>
-
-struct Stack {
-    size_t size;
-    size_t capacity;
-    void* data;
-};
-
-void stack_init(struct Stack* stack, size_t size);
-void stack_push(struct Stack* stack, void* data, size_t len);
-void* stack_pop(struct Stack* stack, size_t len);
-void stack_free(struct Stack* stack);
-
-void stack_push_int(struct Stack* stack, int value); 
-bool stack_pop_int(struct Stack* stack, int* value);
-
-#endif
diff --git a/lib/xfuncs.c b/lib/xfuncs.c
new file mode 100644
index 0000000..43242de
--- /dev/null
+++ b/lib/xfuncs.c
@@ -0,0 +1,49 @@
+#include "lslib.h"
+
+#include <pwd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+void* xalloc(size_t size) {
+	void *ptr = malloc(size);
+	if (ptr == NULL && size != 0) die();
+	return ptr;
+}
+
+void* xrealloc(void* ptr, size_t size) {
+	ptr = realloc(ptr, size);
+	if (ptr == NULL && size != 0) die();
+    return ptr;
+}
+
+void* xzalloc(size_t size) {
+    void* ptr = xalloc(size);
+    memset(ptr, 0, size);
+    return ptr;
+}
+
+void xsetenv(const char *name, const char *value) {
+	if (setenv(name, value, 1))
+        error("cannot set env");
+}
+
+void xsetuid(uid_t uid) {
+    if (setuid(uid))
+        error("cannot set uid");
+}
+
+void xsetgid(gid_t gid) {
+    if (setgid(gid))
+        error("cannot set gid");
+}
+
+struct passwd* xgetpwnam(char* name) {
+    struct passwd* pw;
+    pw = getpwnam(name);
+
+    if (!pw)
+        error("cannot get user: '%s'", name);
+
+    return pw;
+}
diff --git a/readme.md b/readme.md
index 3e34252..2212dd2 100644
--- a/readme.md
+++ b/readme.md
@@ -5,7 +5,7 @@ A terrible busybox/gnu coreutils clone.
 
 Currently the only supported commands are: 
 `dd`, `cat`, `yes`, `echo`, `printf`, `id`, `groups`, `ls`, `tail`, `head`, `ed`, `tee`, `true`, `false`, `tee`, `whoami`, 
-`wc`, `xargs`, `tac`, `rm`, `cp`, `mkdir`, `mv`, `grep`, `chown`, `chmod`, `sync`
+`wc`, `xargs`, `tac`, `rm`, `cp`, `mkdir`, `mv`, `grep`, `chown`, `chmod`, `sync`, `su`
  
 ## How to
 
diff --git a/src/command.h b/src/command.h
index 7827174..3a84784 100644
--- a/src/command.h
+++ b/src/command.h
@@ -29,5 +29,6 @@ COMMAND(grep);
 COMMAND(chown_cmd);
 COMMAND(chmod_cmd);
 COMMAND(sync_cmd);
+COMMAND(su);
 
 #endif
diff --git a/src/main.c b/src/main.c
index 1897f5c..7db2135 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,5 +1,4 @@
 #include "command.h"
-#include "convert.h"
 #include "lslib.h"
 
 #include <stdlib.h>
@@ -23,7 +22,7 @@ int main (ARGUMENTS) {
         if (argc < 2) {
             printf("usage: lazysphere [function [arguments]...]\n\n");
             printf("currently defined functions:\n");
-            printf("\tdd, cat, yes, echo, printf, id, groups, ls, tail, head, ed, tee, true, false, tee, whoami, wc, xargs, tac, rm, cp, mkdir, mv, grep, chown, chmod, sync\n");
+            printf("\tdd, cat, yes, echo, printf, id, groups, ls, tail, head, ed, tee, true, false, tee, whoami, wc, xargs, tac, rm, cp, mkdir, mv, grep, chown, chmod, sync, su\n");
             return EXIT_SUCCESS;
         }
         argc--;
@@ -91,6 +90,8 @@ int main (ARGUMENTS) {
         return chmod_cmd(NEXT_ARGS);
     } else if (streql(cmd, "sync")) {
         return sync_cmd(NEXT_ARGS);
+    } else if (streql(cmd, "su")) {
+        return su(NEXT_ARGS);
     } else {
         fprintf(stderr, "lazysphere: invalid command %s\n", cmd);
         return EXIT_FAILURE;