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CAPGET(2)		   Linux Programmers Manual		    CAPGET(2)

       capget, capset - set/get capabilities of thread(s)

       #undef _POSIX_SOURCE

       int capget(cap_user_header_t hdrp, cap_user_data_t datap);

       int capset(cap_user_header_t hdrp, const cap_user_data_t datap);

       As of Linux 2.2, the power of the superuser (root) has been partitioned
       into a set of discrete capabilities.  Each thread has a set  of	effec
       tive  capabilities  identifying which capabilities (if any) it may cur
       rently exercise.  Each thread also has a set of	inheritable  capabili
       ties that may be passed through an execve(2) call, and a set of permit
       ted capabilities that it can make effective or inheritable.

       These two functions are the raw kernel interface for getting  and  set
       ting  thread capabilities.  Not only are these system calls specific to
       Linux, but the kernel API is likely to change and use  of  these  func
       tions  (in  particular the format of the cap_user_*_t types) is subject
       to change with each kernel revision.

       The portable interfaces are  cap_set_proc(3)  and  cap_get_proc(3);  if
       possible  you should use those interfaces in applications.  If you wish
       to use the Linux extensions in applications, you should use the easier-
       to-use interfaces capsetp(3) and capgetp(3).

   Current details
       Now that you have been warned, some current kernel details.  The struc
       tures are defined as follows.

	   #define _LINUX_CAPABILITY_VERSION_1	0x19980330
	   #define _LINUX_CAPABILITY_U32S_1	1

	   #define _LINUX_CAPABILITY_VERSION_2	0x20071026
	   #define _LINUX_CAPABILITY_U32S_2	2

	   typedef struct __user_cap_header_struct {
	      __u32 version;
	      int pid;
	   } *cap_user_header_t;

	   typedef struct __user_cap_data_struct {
	      __u32 effective;
	      __u32 permitted;
	      __u32 inheritable;
	   } *cap_user_data_t;

       The calls will fail with the error EINVAL, and set the version field of
       hdrp to the kernel preferred value of _LINUX_CAPABILITY_VERSION_?  when
       an unsupported version value is specified.  In this way, one can  probe
       what  the  current  preferred capability revision is.  Kernels prior to
       2.6.25 prefer 32-bit capabilities with  version	_LINUX_CAPABILITY_VER
       SION_1,	and  kernels  2.6.25+  prefer 64-bit capabilities with version
       _LINUX_CAPABILITY_VERSION_2.  Note, 64-bit  capabilities  use  datap[0]
       and datap[1], whereas 32-bit capabilities only use datap[0].

       Another	change	affecting the behavior of these system calls is kernel
       support for file capabilities (VFS capability support).	 This  support
       is currently a compile time option (added in kernel 2.6.24).

       For  capget()  calls,  one can probe the capabilities of any process by
       specifying its process ID with the hdrp->pid field value.

   With VFS Capability Support
       VFS Capability support creates a file-attribute method for adding capa
       bilities  to  privileged  executables.	This privilege model obsoletes
       kernel support for one process asynchronously setting the  capabilities
       of  another.   That  is,  with VFS support, for capset() calls the only
       permitted values for hdrp->pid are 0 or getpid(2),  which  are  equiva

   Without VFS Capability Support
       When  the  kernel does not support VFS capabilities, capset() calls can
       operate on the capabilities of the thread specified by the pid field of
       hdrp  when  that  is  non-zero,	or  on the capabilities of the calling
       thread if pid is 0.  If pid refers to a single-threaded	process,  then
       pid can be specified as a traditional process ID; operating on a thread
       of a multithreaded process requires a thread ID of the type returned by
       gettid(2).   For  capset(),  pid  can  also be: -1, meaning perform the
       change on all threads except the caller and init(8); or	a  value  less
       than -1, in which case the change is applied to all members of the pro
       cess group whose ID is -pid.

       For details on the data, see capabilities(7).

       On success, zero is returned.  On error, -1 is returned, and  errno  is
       set appropriately.

       EFAULT Bad  memory  address.  hdrp must not be NULL.  datap may only be
	      NULL when the user is trying to determine the preferred capabil
	      ity version format supported by the kernel.

       EINVAL One of the arguments was invalid.

       EPERM  An attempt was made to add a capability to the Permitted set, or
	      to set a capability in the Effective or Inheritable sets that is
	      not in the Permitted set.

       EPERM  The  caller attempted to use capset() to modify the capabilities
	      of a thread other than itself, but lacked sufficient  privilege.
	      For  kernels  supporting VFS capabilities, this is never permit
	      ted.  For kernels lacking VFS support, the CAP_SETPCAP  capabil
	      ity  is  required.   (A  bug in kernels before 2.6.11 meant that
	      this error could also occur if a thread without this  capability
	      tried to change its own capabilities by specifying the pid field
	      as a non-zero value (i.e.,  the  value  returned	by  getpid(2))
	      instead of 0.)

       ESRCH  No such thread.

       These system calls are Linux-specific.

       The portable interface to the capability querying and setting functions
       is provided by the libcap library and is available here:

       clone(2), gettid(2), capabilities(7)

       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2008-07-14			     CAPGET(2)

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