intro.2

操作系统设计与实现源码

58  EADDRINUSE  Address in use

59  ECONNREFUSED  Connection refused

60  ECONNRESET  Connection reset

61  ETIMEDOUT  Connection timed out

62  EURG  Urgent data present

63  ENOURG  No urgent data present

64  ENOTCONN  No connection

65  ESHUTDOWN  Already shutdown

66  ENOCONN  No such connection

67  EINPROGRESS  Operation now in progress

68  EALREADY  Operation already in progress





4BSD                              June 30, 1986                              5



INTRO(2)                  Minix Programmer's Manual                   INTRO(2)


DEFINITIONS

     Process ID
          Each active process in  the  system  is  uniquely  identified  by  a
          positive  integer called a process ID.  The range of this ID is from
          1 to 29999.  The special process with process  ID  1  is  init,  the
          ancestor of all processes.

     Parent process ID
          A new process  is  created  by  a  currently  active  process;  (see
          fork(2)).   The  parent process ID of a process is the process ID of
          its creator, unless the creator dies, then init becomes  the  parent
          of the orphaned process.

     Process Group ID
          Each active  process  is  a  member  of  a  process  group  that  is
          identified  by a positive integer called the process group ID.  This
          is the process ID of the group leader.  This  grouping  permits  the
          signaling of related processes (see kill(2)).

     Real User ID and Real Group ID
          Each user on the system is identified by a positive  integer  termed
          the real user ID.

          Each user is also a member of one or  more  groups.   One  of  these
          groups  is  distinguished  from  others  and  used  in  implementing
          accounting facilities.  The positive integer corresponding  to  this
          distinguished  group  is  termed the real group ID.  (Under standard
          Minix this is the only group a process can be a member of.)

          All processes have a real user ID and  real  group  ID.   These  are
          initialized  from  the  equivalent  attributes  of  the process that
          created it.

     Effective User Id, Effective Group Id, and Access Groups
          Access to  system  resources  is  governed  by  three  values:   the
          effective  user  ID,  the  effective  group ID, and the group access
          list.

          The effective user ID and  effective  group  ID  are  initially  the
          process's  real  user ID and real group ID respectively.  Either may
          be modified through execution of a set-user-ID or set-group-ID  file
          (possibly by one its ancestors) (see execve(2)).

          The group access list is an additional set of group ID's  used  only
          in  determining resource accessibility.  Access checks are performed
          as described below in  ``File  Access  Permissions''.   The  maximum
          number  of  additional group ID's is NGROUPS_MAX.  For Minix this is
          0, but Minix-vmd supports a list of up to 16 additional group  ID's.
          (Also known as ``supplemental'' group ID's.)


4BSD                              June 30, 1986                              6



INTRO(2)                  Minix Programmer's Manual                   INTRO(2)


     Super-user
          A process is recognized as  a  super-user  process  and  is  granted
          special privileges if its effective user ID is 0.

     Descriptor
          An integer  assigned  by  the  system  when  a  file  or  device  is
          referenced  by open(2), dup(2) or fcntl(2) which uniquely identifies
          an access path to that file or device from a given process or any of
          its children.

     File Descriptor
          Older, and often used name for a descriptor.

     File Name
          Names consisting of up to NAME_MAX characters may be used to name an
          ordinary  file, special file, or directory.  NAME_MAX is the maximum
          of the maximum file name lengths  of  the  supported  file  systems.
          Excess  characters are ignored when too long file names are used for
          files in a given file system.  The maximum file name length  of  the
          V1  and  V2  file  systems  is  14 characters.  The Minix-vmd "flex"
          variants of V1 and V2 have a 60 character maximum.

          The characters in a file name may assume any value representable  in
          eight bits excluding 0 (null) and the ASCII code for / (slash).

          Note that it is generally unwise to use one  of  \'"<>();~$^&*|{}[]?
          as  part  of  file  names because of the special meaning attached to
          these characters by the shell.

     Path Name
          A path name is a null-terminated character string starting  with  an
          optional  slash  (/),  followed  by  zero  or  more  directory names
          separated by slashes, optionally followed by a file name.  The total
          length  of a path name must be less than PATH_MAX characters (255 as
          distributed.)

          If a path name begins with a slash, the path search  begins  at  the
          root  directory.   Otherwise,  the  search  begins  from the current
          working directory.  A slash by itself names the root  directory.   A
          null  pathname  is  illegal, use "." to refer to the current working
          directory.

     Directory
          A directory is a special type of file that contains entries that are
          references  to other files.  Directory entries are called links.  By
          convention, a directory contains at  least  two  links,  .  and  ..,
          referred  to  as  dot  and  dot-dot respectively.  Dot refers to the
          directory itself and dot-dot refers to its parent directory.




4BSD                              June 30, 1986                              7



INTRO(2)                  Minix Programmer's Manual                   INTRO(2)


     Root Directory and Current Working Directory
          Each process has associated with it a concept of  a  root  directory
          and  a  current  working directory for the purpose of resolving path
          name searches.  A process's root directory  need  not  be  the  root
          directory of the root file system.

     File Access Permissions
          Every file in the file system  has  a  set  of  access  permissions.
          These  permissions  are  used  in  determining whether a process may
          perform a requested operation on the file (such as  opening  a  file
          for writing).  Access permissions are established at the time a file
          is created.  They may be changed at  some  later  time  through  the
          chmod(2) call.

          File access is broken down according to whether a file may be: read,
          written, or executed.  Directory files use the execute permission to
          control if the directory may be searched.

          File access permissions are interpreted by the system as they  apply
          to  three  different  classes of users: the owner of the file, those
          users  in  the  file's  group,  anyone  else.   Every  file  has  an
          independent  set  of  access  permissions for each of these classes.
          When an access check is  made,  the  system  decides  if  permission
          should  be  granted by checking the access information applicable to
          the caller.

          Read, write, and execute/search permissions on a file are granted to
          a process if:

          The process's effective user ID is that of the super-user.

          The process's effective user ID matches the user ID of the owner  of
          the file and the owner permissions allow the access.

          The process's effective user ID does not match the user  ID  of  the
          owner  of  the  file,  and  either  the process's effective group ID
          matches the group ID of the file, or the group ID of the file is  in
          the process's group access list, and the group permissions allow the
          access.

          Neither the effective user ID  nor  effective  group  ID  and  group
          access list of the process match the corresponding user ID and group
          ID of the file,  but  the  permissions  for  ``other  users''  allow
          access.

          Otherwise, permission is denied.






4BSD                              June 30, 1986                              8



INTRO(2)                  Minix Programmer's Manual                   INTRO(2)


SEE ALSO
     intro(3), strerror(3).


















































4BSD                              June 30, 1986                              9