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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | DEBUGGING | SEE ALSO | COLOPHON |
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PROCPS(3) Library Functions Manual PROCPS(3)
procps - API to access system level information in the /proc
filesystem
Five distinct interfaces are represented in this synopsis and
named after the files they access in the /proc pseudo filesystem:
diskstats, meminfo, slabinfo, stat and vmstat.
#include <libproc2/named_interface.h>
int procps_new (struct info **info);
int procps_ref (struct info *info);
int procps_unref (struct info **info);
struct result *procps_get (
struct info *info,
[ const char *name, ] diskstats api only
enum item item);
struct stack *procps_select (
struct info *info,
[ const char *name, ] diskstats api only
enum item *items,
int numitems);
struct reaped *procps_reap (
struct info *info,
[ enum reap_type what, ] stat api only
enum item *items,
int numitems);
struct stack **procps_sort (
struct info *info,
struct stack *stacks[],
int numstacked,
enum item sortitem,
enum sort_order order);
The above functions and structures are generic but the
specific named_interface would also be part of any
identifiers. For example, ‘procps_new’ would actually be
‘procps_meminfo_new’ and ‘info’ would really be
‘diskstats_info’, etc.
The same named_interface is used in each header file name with
an appended ‘.h’ suffix.
Link with -lproc2.
Overview
Central to these interfaces is a simple ‘result’ structure
reflecting an ‘item’ plus its value (in a union with standard C
language types as members). All ‘result’ structures are
automatically allocated and provided by the library.
By specifying an array of ‘items’, these structures can be
organized as a ‘stack’, potentially yielding many results with a
single function call. Thus, a ‘stack’ can be viewed as a variable
length record whose content and order is determined solely by the
user.
As part of each interface there are two unique enumerators. The
‘noop’ and ‘extra’ items exist to hold user values. They are
never set by the library, but the ‘extra’ result will be zeroed
with each library interaction.
The named_interface header file will be an essential document
during user program development. There you will find available
items, their return type (the ‘result’ struct member name) and the
source for such values. Additional enumerators and structures are
also documented there.
Usage
The following would be a typical sequence of calls to these
interfaces.
1. procps_new()
2. procps_get(), procps_select() or procps_reap()
3. procps_unref()
The get function is used to retrieve a ‘result’ structure for a
single ‘item’. Alternatively, a GET macro is available when only
the return value is of interest.
The select function can retrieve multiple ‘result’ structures in a
single ‘stack’.
For unpredictable variable outcomes, the diskstats, slabinfo and
stat interfaces export a reap function. It is used to retrieve
multiple ‘stacks’ each containing multiple ‘result’ structures.
Optionally, a user may choose to sort those results.
To exploit any ‘stack’, and access individual ‘result’ structures,
a relative_enum is required as shown in the VAL macro defined in
the header file. Such values could be hard coded as: 0 through
numitems-1. However, this need is typically satisfied by creating
your own enumerators corresponding to the order of the ‘items’
array.
Caveats
The new, ref, unref, get and select functions are available in all
five interfaces.
For the new and unref functions, the address of an info struct
pointer must be supplied. With new it must have been initialized
to NULL. With unref it will be reset to NULL if the reference
count reaches zero.
In the case of the diskstats interface, a name parameter on the
get and select functions identifies a disk or partition name
For the stat interface, a what parameter on the reap function
identifies whether data for just CPUs or both CPUs and NUMA nodes
is to be gathered.
When using the sort function, the parameters stacks and numstacked
would normally be those returned in the ‘reaped’ structure.
Functions Returning an ‘int’
An error will be indicated by a negative number that is always the
inverse of some well known errno.h value.
Success is indicated by a zero return value. However, the ref and
unref functions return the current info structure reference count.
Functions Returning an ‘address’
An error will be indicated by a NULL return pointer with the
reason found in the formal errno value.
Success is indicated by a pointer to the named structure.
To aid in program development, there is a provision that can help
ensure ‘result’ member references agree with library expectations.
It assumes that a supplied macro in the header file is used to
access the ‘result’ value.
This feature can be activated through either of the following
methods and any discrepancies will be written to stderr.
1) Add CFLAGS='-DXTRA_PROCPS_DEBUG' to any other ./configure
options employed.
2) Add #include <libproc2/xtra-procps-debug.h> to any program
after the named interface includes.
This verification feature incurs substantial overhead. Therefore,
it is important that it not be activated for a production/release
build.
procps_misc(3), procps_pids(3), proc(5).
This page is part of the procps-ng (/proc filesystem utilities)
project. Information about the project can be found at
⟨https://gitlab.com/procps-ng/procps⟩. If you have a bug report
for this manual page, see
⟨https://gitlab.com/procps-ng/procps/blob/master/Documentation/bugs.md⟩.
This page was obtained from the project's upstream Git repository
⟨https://gitlab.com/procps-ng/procps.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-07-30.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
procps-ng 2024-01-22 PROCPS(3)
Pages that refer to this page: procps_misc(3), procps_pids(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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