procps/doc/procps_misc.3

.\" (C) Copyright 2020 Craig Small <csmall@dropbear.xyz>
.\"
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.\"
.TH PROCPS_MISC 3 2020-12-21 "libproc-2"
.\" Please adjust this date whenever revising the manpage.
.\"
.SH NAME
procps_misc \- API to system information in the /proc filesystem
.SH SYNOPSIS
.nf
.B #include <proc/namespace.h>
.PP
.BI "int procps_ns_get_id(const char * " name ");"
.BI "const char *procps_ns_get_name(const int " id ");"
.BI "int procps_ns_read_pid(const int " pid ", struct procps_namespaces * " nsp ");"
.PP
.B #include <proc/sysinfo.h>
.PP
.B long procps_cpu_count(void);
.B long procps_hertz_get(void);
.BI "int procps_loadavg(double * " av1 ", double * " av5 ", double * " av15 ");"
.B unsigned int procps_pid_length(void);
.PP
.B #include <proc/version.h>
.PP
.B int procps_linux_version(void);
.sp
Link with \fI\-lprocps\fP.
.SH DESCRIPTION
This manual page describes the miscellaneous API functions of the
.B procps
library.

.BR procps_cpu_count ()
returns the number of CPUs that are currently online. On most systems returns
the value of
.BI sysconf( _SC_NPROCESSORS_ONLY )
or assumed to be \fI1\fR.

.BR procps_hertz_get ()
returns the number of clock ticks per second. On most systems returns the
value of
.BI sysconf( _SC_CLK_TCK )
or assumed to be \fI100\fR. Divide certain values returned in the
in the \fI/proc\fR filesystem by this value to convert from ticks to seconds.

.BR procps_loadavg ()
Fetches the system load average and puts the 1, 5 and 15 minute averages into
the locations in the given pointers. If the relevant pointer is \fINULL\fR then
.BR procps_loadavg ()
will not set that value.

.BR procps_pid_length ()
Returns the maximum string length for a PID on the system. For example, if the largest
possible PID value on was 123, then the length would be 3. If the file
\fI/proc/sys/kernel/pid_max\fR is unreadable, the value is assumed to be  \fI5\fR.

.BR procps_linux_version ()
returns the current Linux version as an integer. On non-Linux systems that
have an emulated proc filesystem this function returns the version of the
Linux emulation instead.
The Linux version consists of a triple of positive integers representing
the major, minor and patch versions of the kernel.
.PP
The library provides 3 macros for separating out the components.
.RS 4
.TP 1.2i
.BR LINUX_VERSION_MAJOR (ver)
Extract the major component from the given version integer.
.TP
.BR LINUX_VERSION_MINOR (ver)
Extract the minor component from the given version integer.
.TP
.BR LINUX_VERSION_PATCH (ver)
Extract the patch component from the given version integer.
.RE
.PP
To encode a given Linux version, such as using it to compare against the current
version, use the following macro:
.TP
.BI LINUX_VERSION( major , minor , patch )
.PP
.BR procps_ns_get_id ()
finds the ID of the namespace for the given namespace name.

.BR procps_ns_get_name ()
finds the name of the namespace of the given integer ID.

.BR procps_ns_read_pid ()
puts the inodes for the namespaces of the given process into
the array pointed to \fInsp\fR.

.SH RETURN VALUE
For
.BR procps_cpu_count "() , " procps_hertz_get "() and " procps_pid_length ()
see the \fBDESCRIPTION\fR section for return values.

.BR procps_loadavg ()
returns 0 on success. On failure, it
returns a negative integer to one of the values defined below.
.TP
.B -ERANGE
Unable to parse the loadavg file.
.PP

.BR procps_linux_version ()
returns a positive integer encoding the Linux version if successful. Otherwise
returns a negative integer to one of the values defined below.
.TP
.B -EIO
The procps library was unable to read the osrelease file.
.TP
.B -ERANGE
Unable to parse the osrelease file.
.PP
.BR procps_linux_version ()
may also return any (negated) value that \fBfopen\fR() may set errno to.

.BR procps_ns_get_id ()
returns an integer for the namespace ID for the given name or
.B \-EINVAL
for an invalid input or an unknown namespace name.

.BR procps_ns_get_name ()
returns a statically allocated string containing the name of the
namespace for the given ID. If the name is not found the function
returns
.B NULL

.BR procps_ns_read_pid ()
Returns 0 on success and \fB\-EINVAL\fR on failure.

.SH FILES
.TP
.I /proc/loadavg
The raw values for load average.
.TP
.I /proc/sys/kernel/osrelease
Contains the release version of the Linux kernel or proc filesystem.
.TP
.I /proc/sys/kernel/pid_max
Contains the value at which PIDs wrap around, one greater than the maximum PID value.
.IB /proc/ PID /ns
contains the set of namespaces for a particular \fBPID\fR.

.SH BUGS
Due to the way the three numbers are encoded into a single integer,
.BR procps_linux_version ()
and the associated macros assume 255 for the maximum value for the
minor and patch level and 32767 (hex 0x7fff) for the maximum value
for the major version. In other words, when Linux v 32768.0.0 comes
out, this function will break.
.\" Maj/6yr - In 7452 we'll think of something

.SH SEE ALSO
.BR fopen (3),
.BR sysconf (3),
.BR proc (5).