History

History

Multi user

Old School

UNIX FEATURES

KERNEL / SHELL

Kernel / ShELL

Kernel / Shell

User / Kernel Space

C

void main()
{
  printf("Hello world\n");
}

toki (~/unix) > gcc helloworld.c

toki (~/unix) > ./a.out
Hello world
toki (~/unix) > ls -ld a.out 

-rwxr-xr-x 1 chris lokku 8515 Dec 12 13:07 a.out*

toki (~/unix) > ldd a.out 
	linux-vdso.so.1 =>  (0x00007fff585fe000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5905530)
	/lib64/ld-linux-x86-64.so.2 (0x00007f5905916000)

Hello world 2

void main()
{
  write(0, "Hello world\n", sizeof("Hello world\n"));
}

toki (~/unix) > ./helloworld2
Hello world

fork / exec

FORK()

void main()
{
  int ret;b

  ret = fork();

  printf("Hello world (pid %d).  ret = %d\n", getpid(), ret);
}

toki (~/unix) > ./1         
Hello world (pid 11450).  ret = 11451
Hello world (pid 11451).  ret = 0
toki (~/unix) > 

File descriptors

Processes

Processes

THREADS

Process MEmory to Kernel Memory

BINARY

BINARY

C

Characters

CODE!

struct listing {
  char teaser[10];
  int rooms;
  int bedrooms;
};

void main()
{
  int i;
  struct listing li;

  memset(&li, 0, sizeof(li));
  strcpy(li.teaser, "ateaser");
  li.rooms = 5;
  li.bedrooms = 3;
  
  char *pt = (char *)&li;

  for (i = 0 ; i < sizeof(struct listing) ; i++) {
    printf("%c (%hhu)\n", *pt, *pt);
    pt++;
  }
}

OUTPUT

a (97)
t (116)
e (101)
a (97)
s (115)
e (101)
r (114)
 (0)
 (0)
 (0)
 (0)
 (0)
 (5)
 (0)
 (0)
 (0)
 (3)
 (0)
 (0)
 (0)

UNIX FILESYSTEM

STAT

Directory system

man fstat

         struct stat {
             dev_t     st_dev;     /* ID of device containing file */
             ino_t     st_ino;     /* inode number */
             mode_t    st_mode;    /* protection */
             nlink_t   st_nlink;   /* number of hard links */
             uid_t     st_uid;     /* user ID of owner */
             gid_t     st_gid;     /* group ID of owner */
             dev_t     st_rdev;    /* device ID (if special file) */
             off_t     st_size;    /* total size, in bytes */
             blksize_t st_blksize; /* blocksize for file system I/O */
             blkcnt_t  st_blocks;  /* number of 512B blocks allocated 
             time_t    st_atime;   /* time of last access */
             time_t    st_mtime;   /* time of last modification */
             time_t    st_ctime;   /* time of last status change */
         };

man readdir

         struct dirent {
             ino_t          d_ino;       /* inode number */
             off_t          d_off;       /* offset to the next */
             unsigned short d_reclen;    /* length of this record */
             unsigned char  d_type;      /* type of file */
             char           d_name[256]; /* filename */
         };

Filesystem Layout