xref: /dragonfly/lib/libc/sys/ktrace.2 (revision 8f2ce533) 
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28.\"     @(#)ktrace.2	8.1 (Berkeley) 6/4/93
29.\" $FreeBSD: src/lib/libc/sys/ktrace.2,v 1.9.2.7 2001/12/14 18:34:01 ru Exp $
30.\"
31.Dd November 24, 2019
32.Dt KTRACE 2
33.Os
34.Sh NAME
35.Nm ktrace
36.Nd process tracing
37.Sh LIBRARY
38.Lb libc
39.Sh SYNOPSIS
40.In sys/param.h
41.In sys/time.h
42.In sys/ktrace.h
43.Ft int
44.Fn ktrace "const char *tracefile" "int ops" "int trpoints" "int pid"
45.Sh DESCRIPTION
46The
47.Fn ktrace
48function enables or disables tracing of one or more processes.
49Users may only trace their own processes.
50By default only the super-user can trace setuid or setgid programs.
51This restriction can be removed by setting the sysctl
52.Va kern.ktrace_suid
53to a non-zero value.
54.Pp
55The
56.Fa tracefile
57gives the pathname of the file to be used for tracing.
58The file must exist and be a regular file writable by the calling process.
59All trace records are always appended to the file,
60so the file must be truncated to zero length to discard
61previous trace data.
62If tracing points are being disabled (see
63.Dv KTROP_CLEAR
64below),
65.Fa tracefile
66may be NULL.
67.Pp
68The
69.Fa ops
70parameter specifies the requested ktrace operation.
71The defined operations are:
72.Pp
73.Bl -tag -width KTRFAC_SYSCALLXXXXXX -compact -offset indent
74.It Dv KTROP_SET
75Enable trace points specified in
76.Fa trpoints .
77.It Dv KTROP_CLEAR
78Disable trace points specified in
79.Fa trpoints .
80.It Dv KTROP_CLEARFILE
81Stop all tracing.
82.It Dv KTRFLAG_DESCEND
83The tracing change should apply to the
84specified process and all its current children.
85.El
86.Pp
87The
88.Fa trpoints
89parameter specifies the trace points of interest.
90The defined trace points are:
91.Pp
92.Bl -tag -width KTRFAC_SYSCALLXXXXXX -compact -offset indent
93.It Dv KTRFAC_SYSCALL
94Trace system calls.
95.It Dv KTRFAC_SYSRET
96Trace return values from system calls.
97.It Dv KTRFAC_NAMEI
98Trace name lookup operations.
99.It Dv KTRFAC_GENIO
100Trace all I/O (note that this option can
101generate much output).
102.It Dv KTRFAC_PSIG
103Trace posted signals.
104.It Dv KTRFAC_CSW
105Trace context switch points.
106.It Dv KTRFAC_INHERIT
107Inherit tracing to future children.
108.El
109.Pp
110Each tracing event outputs a record composed of a generic header
111followed by a trace point specific structure.
112The generic header is:
113.Bd -literal
114struct ktr_header {
115	int	ktr_len;		/* length of buf */
116	short	ktr_type;		/* trace record type */
117	pid_t	ktr_pid;		/* process id */
118	char	ktr_comm[MAXCOMLEN+1];	/* command name */
119	struct	timeval ktr_time;	/* timestamp */
120	caddr_t	ktr_buf;
121};
122.Ed
123.Pp
124The
125.Va ktr_len
126field specifies the length of the
127.Va ktr_type
128data that follows this header.
129The
130.Va ktr_pid
131and
132.Va ktr_comm
133fields specify the process and command generating the record.
134The
135.Va ktr_time
136field gives the time (with microsecond resolution)
137that the record was generated.
138The
139.Va ktr_buf
140is an internal kernel pointer and is not useful.
141.Pp
142The generic header is followed by
143.Va ktr_len
144bytes of a
145.Va ktr_type
146record.
147The type specific records are defined in the
148.In sys/ktrace.h
149include file.
150.Sh RETURN VALUES
151.Rv -std ktrace
152.Sh ERRORS
153The
154.Fn ktrace
155will fail if:
156.Bl -tag -width Er
157.It Bq Er ENOTDIR
158A component of the path prefix is not a directory.
159.It Bq Er ENAMETOOLONG
160A component of a pathname exceeded 255 characters,
161or an entire path name exceeded 1023 characters.
162.It Bq Er ENOENT
163The named tracefile does not exist.
164.It Bq Er EACCES
165Search permission is denied for a component of the path prefix.
166.It Bq Er ELOOP
167Too many symbolic links were encountered in translating the pathname.
168.It Bq Er EIO
169An I/O error occurred while reading from or writing to the file system.
170.It Bq Er ENOSYS
171The kernel was not compiled with
172.Nm
173support.
174.El
175.Sh SEE ALSO
176.Xr kdump 1 ,
177.Xr ktrace 1 ,
178.Xr utrace 2
179.Sh HISTORY
180A
181.Fn ktrace
182function call first appeared in
183.Bx 4.4 .
184