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NAME
capget, capset - set/get capabilities
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. Every thread has a set of
effective capabilities identifying which capabilities (if any) it may
currently exercise. Every thread also has a set of inheritable
capabilities 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 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 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
structs are defined as follows.
#define _LINUX_CAPABILITY_VERSION 0x19980330
typedef struct __user_cap_header_struct {
int version;
int pid;
} *cap_user_header_t;
typedef struct __user_cap_data_struct {
int effective;
int permitted;
int inheritable;
} *cap_user_data_t;
The calls will return EINVAL, and set the version field of hdrp to
_LINUX_CAPABILITY_VERSION when another version was specified.
The calls 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.
ERRORS
EFAULT Bad memory address. Neither of hdrp and datap may be NULL.
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;
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:
ftp://ftp.kernel.org/pub/linux/libs/security/linux-privs
SEE ALSO
clone(2), gettid(2), capabilities(7)
COLOPHON
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be found at http://www.kernel.org/doc/man-pages/.