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           #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);


           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 system calls 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  sys-
           tem  calls (in particular the format of the cap_user_*_t types) is sub-
           ject to extension with each kernel revision, but old programs will keep
           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  effective,  permitted, and inheritable fields are bit masks of the
           capabilities defined in capabilities(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
           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 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 get-
           tid(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).


           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.


           EFAULT Bad  memory  address.  hdrp must not be NULL.  datap may be NULL
                  only 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 nonzero value  (i.e.,  the  value  returned  by  getpid(2))

    Linux 2013-03-11 CAPGET(2)


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