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



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

SYNOPSIS
       #undef _POSIX_SOURCE
       #include <&lt;sys/capability.h>&gt;

       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  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-&gt;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-&gt;pid are 0 or getpid(2),  which  are  equiva-
       lent.

   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
       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.

ERRORS
       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.

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 3.05 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)