xref: /dragonfly/lib/libc/sys/ktrace.2 (revision 55f88487) 
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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 April 4, 2023
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_SYSCTL
107Trace sysctls.
108.It Dv KTRFAC_INHERIT
109Inherit tracing to future children.
110.El
111.Pp
112Each tracing event outputs a record composed of a generic header
113followed by a trace point specific structure.
114The generic header is:
115.Bd -literal
116struct ktr_header {
117	int	ktr_len;		/* length of buf */
118	short	ktr_type;		/* trace record type */
119	pid_t	ktr_pid;		/* process id */
120	char	ktr_comm[MAXCOMLEN+1];	/* command name */
121	struct	timeval ktr_time;	/* timestamp */
122	caddr_t	ktr_buf;
123};
124.Ed
125.Pp
126The
127.Va ktr_len
128field specifies the length of the
129.Va ktr_type
130data that follows this header.
131The
132.Va ktr_pid
133and
134.Va ktr_comm
135fields specify the process and command generating the record.
136The
137.Va ktr_time
138field gives the time (with microsecond resolution)
139that the record was generated.
140The
141.Va ktr_buf
142is an internal kernel pointer and is not useful.
143.Pp
144The generic header is followed by
145.Va ktr_len
146bytes of a
147.Va ktr_type
148record.
149The type specific records are defined in the
150.In sys/ktrace.h
151include file.
152.Sh RETURN VALUES
153.Rv -std ktrace
154.Sh ERRORS
155The
156.Fn ktrace
157will fail if:
158.Bl -tag -width Er
159.It Bq Er ENOTDIR
160A component of the path prefix is not a directory.
161.It Bq Er ENAMETOOLONG
162A component of a pathname exceeded 255 characters,
163or an entire path name exceeded 1023 characters.
164.It Bq Er ENOENT
165The named tracefile does not exist.
166.It Bq Er EACCES
167Search permission is denied for a component of the path prefix.
168.It Bq Er ELOOP
169Too many symbolic links were encountered in translating the pathname.
170.It Bq Er EIO
171An I/O error occurred while reading from or writing to the file system.
172.It Bq Er ENOSYS
173The kernel was not compiled with
174.Nm
175support.
176.El
177.Sh SEE ALSO
178.Xr kdump 1 ,
179.Xr ktrace 1 ,
180.Xr utrace 2 ,
181.Xr sysctl 8
182.Sh HISTORY
183A
184.Fn ktrace
185function call first appeared in
186.Bx 4.4 .
187