man-pages/man2/capget.2

.\"
.\" $Id: capget.2,v 1.4 1999/09/09 16:43:26 morgan Exp $
.\" written by Andrew Morgan <morgan@linux.kernel.org>
.\" may be distributed as per GPL
.\" Modified by David A. Wheeler <dwheeler@ida.org>
.\" Modified 2004-05-27, mtk
.\" Modified 2004-06-21, aeb
.\" FIXME capabilities are actually per-thread
.\"
.TH CAPGET 2 2004-06-21 "Linux 2.6.6" "Linux Programmer's Manual"
.SH NAME
capget, capset \- set/get process capabilities
.SH SYNOPSIS
.B #undef _POSIX_SOURCE
.br
.B #include <sys/capability.h>
.sp
.BI "int capget(cap_user_header_t " hdrp ", cap_user_data_t " datap );
.sp
.BI "int capset(cap_user_header_t " hdrp ", const cap_user_data_t " datap );
.SH DESCRIPTION
As of Linux 2.2, the power of the superuser (root) has been partitioned into
a set of discrete capabilities.
Every process has a set of effective capabilities identifying
which capabilities (if any) it may currently exercise.
Every process also has a set of inheritable capabilities that may be
passed through an
.BR execve (2)
call, and a set of permitted capabilities
that it can make effective or inheritable.
.PP
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
.B cap_user_*_t
types) is subject to change with each kernel revision.
.sp
The portable interfaces are
.BR cap_set_proc (3)
and
.BR 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
.BR capsetp (3)
and 
.BR capgetp (3).
.SS "Current details"
Now that you have been warned, some current kernel details.
The structs are defined as follows.
.sp
.nf
.in +4n
#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;
.fi
.in -4n
.sp
The calls will return EINVAL, and set the version field of
.I hdr
to _LINUX_CAPABILITY_VERSION when another version was specified.

The calls refer to the capabilities of the process indicated by
the pid field of
.I hdr
when that is non-zero, or to the current process otherwise.

For details on the data, see
.BR capabilities (7).
.SH "RETURN VALUE"
On success, zero is returned.  On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EFAULT
Bad memory address. Neither of
.I hdrp
and
.I datap
may be NULL.
.TP
.B EINVAL
One of the arguments was invalid.
.TP
.B 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.
.TP
.B EPERM
The calling process attempted to use
.BR capset ()
to modify the capabilities of a process other than itself,
but lacked sufficient privilege; the
.B CAP_SETPCAP
capability is required.
.TP
.B ESRCH
No such process.
.SH "FURTHER INFORMATION"
The portable interface to the capability querying and setting
functions is provided by the
.B libcap
library and is available from here:
.br
.B ftp://ftp.kernel.org/pub/linux/libs/security/linux-privs
.SH "SEE ALSO"
.\" FIXME add gettid(2), clone(2) once we've explained threads
.BR capabilities (7)