CAPGET(2)						     Linux Programmer's Manual							 CAPGET(2)

NAME

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

SYNOPSIS

       #undef _POSIX_SOURCE
       #include <sys/capability.h>

       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);

DESCRIPTION

       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
       effective capabilities identifying which capabilities (if any) it may currently exercise.  Each thread also has a set of inheritable  capa-
       bilities that may be passed through an execve(2) call, and a set of permitted capabilities that it can make effective or inheritable.

       These  two functions are the raw kernel interface for getting and setting thread capabilities.  Not only are these system calls specific to
       Linux, but the kernel API is likely to change and use of these functions (in particular the format of the cap_user_*_t types) is subject to
       extension with each kernel revision, but old programs will keep working.

       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 structures 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;

       effective, permitted, inheritable are bitmasks of the capabilities defined in capability(7).  Note the CAP_* values  are  bit  indexes  and
       need  to  be  bit-shifted  before  ORing  into the bit fields.  To define the structures for passing to the system call you have to use the
       struct __user_cap_header_struct and struct __user_cap_data_struct names because the typedefs are only pointers.

       Kernels prior to 2.6.25 prefer 32-bit capabilities with version _LINUX_CAPABILITY_VERSION_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 capabilities 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 equivalent.

   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 nonzero, 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 process group whose ID is -pid.

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

RETURN VALUE

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

       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.

ERRORS

       EFAULT Bad memory address.  hdrp must not be NULL.  datap may only be NULL when the user is trying to determine	the  preferred	capability
	      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	permitted.  For kernels lacking VFS support, the CAP_SETPCAP capability 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 nonzero value (i.e., the value returned by getpid(2)) instead of 0.)

       ESRCH  No such thread.

CONFORMING TO

       These system calls are Linux-specific.

NOTES

       The portable interface to the capability querying and setting functions is provided by the libcap library and is available here:
       http://www.kernel.org/pub/linux/libs/security/linux-privs

SEE ALSO

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

COLOPHON

       This  page is part of release 3.25 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								    2009-01-26								 CAPGET(2)