From Linux Man Pages
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 exer-
cise. 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 inter-
faces 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 hdr to _LINUX_CAPABILITY_VERSION when another version
was specified.
The calls operate on the capabilities of the thread specified by the pid field of hdr 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. 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 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.
FURTHER INFORMATION
The portable interface to the capability querying and setting functions is provided by the libcap library and is
available from here:
ftp://ftp.kernel.org/pub/linux/libs/security/linux-privs
RELATED
clone(2), gettid(2), capabilities(7)
CATEGORY