.\"
.\" $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
.\"
.TH CAPGET 2 2004-06-21 "Linux 2.6.6" "Linux Programmer's Manual"
.SH NAME
capget, capset \- set/get 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 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
.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
.I version
field of
.I hdr
to _LINUX_CAPABILITY_VERSION when another version was specified.

The calls operate on the capabilities of the thread specified by the
.I pid
field of
.I hdr
when that is non-zero, or on the capabilities of the calling thread if
.I pid
is 0.
If
.I pid
refers to a single-threaded process, then
.I 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
.BR gettid (2).
For
.BR capset (),
.I pid
can also be: \-1, meaning perform the change on all threads except the
caller and
.IR 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 \-\fIpid\fP.

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 caller attempted to use
.BR capset ()
to modify the capabilities of a thread other than itself,
but lacked sufficient privilege; the
.B 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
.I pid
field as a non-zero value (i.e., the value returned by
.BR getpid (2))
instead of 0.)
.TP
.B ESRCH
No such thread.
.SH "CONFORMING TO"
These system calls are Linux specific.
.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"
.BR clone (2),
.BR gettid (2),
.BR capabilities (7)