NAME¶
ktrace
—
process tracing
LIBRARY¶
Standard C Library (libc, -lc)
SYNOPSIS¶
#include
<sys/param.h>
#include
<sys/time.h>
#include
<sys/uio.h>
#include
<sys/ktrace.h>
int
ktrace
(
const
char *tracefile,
int ops,
int trpoints,
int pid);
DESCRIPTION¶
The
ktrace
() system call enables or disables
tracing of one or more processes. Users may only trace their own processes.
Only the super-user can trace setuid or setgid programs.
The
tracefile argument gives the pathname of
the file to be used for tracing. The file must exist and be a regular file
writable by the calling process. All trace records are always appended to the
file, so the file must be truncated to zero length to discard previous trace
data. If tracing points are being disabled (see KTROP_CLEAR below),
tracefile may be NULL.
The
ops argument specifies the requested ktrace
operation. The defined operations are:
KTROP_SET |
Enable trace points specified in
trpoints. |
KTROP_CLEAR |
Disable trace points specified in
trpoints. |
KTROP_CLEARFILE |
Stop all tracing. |
KTRFLAG_DESCEND |
The tracing change should apply to the specified process and all its
current children. |
The
trpoints argument specifies the trace
points of interest. The defined trace points are:
KTRFAC_SYSCALL |
Trace system calls. |
KTRFAC_SYSRET |
Trace return values from system calls. |
KTRFAC_NAMEI |
Trace name lookup operations. |
KTRFAC_GENIO |
Trace all I/O (note that this option can generate much output). |
KTRFAC_PSIG |
Trace posted signals. |
KTRFAC_CSW |
Trace context switch points. |
KTRFAC_USER |
Trace application-specific events. |
KTRFAC_STRUCT |
Trace certain data structures. |
KTRFAC_SYSCTL |
Trace sysctls. |
KTRFAC_PROCCTOR |
Trace process construction. |
KTRFAC_PROCDTOR |
Trace process destruction. |
KTRFAC_CAPFAIL |
Trace capability failures. |
KTRFAC_INHERIT |
Inherit tracing to future children. |
Each tracing event outputs a record composed of a generic header followed by a
trace point specific structure. The generic header is:
struct ktr_header {
int ktr_len; /* length of buf */
short ktr_type; /* trace record type */
pid_t ktr_pid; /* process id */
char ktr_comm[MAXCOMLEN+1]; /* command name */
struct timeval ktr_time; /* timestamp */
intptr_t ktr_tid; /* was ktr_buffer */
};
The
ktr_len field specifies the length of the
ktr_type data that follows this header. The
ktr_pid and
ktr_comm fields specify the process and
command generating the record. The
ktr_time
field gives the time (with microsecond resolution) that the record was
generated. The
ktr_tid field holds a thread
id.
The generic header is followed by
ktr_len bytes
of a
ktr_type record. The type specific
records are defined in the
<sys/ktrace.h>
include file.
SYSCTL TUNABLES¶
The following
sysctl(8) tunables influence the
behaviour of
ktrace
():
- kern.ktrace.geniosize
- bounds the amount of data a traced I/O request will log to the trace
file.
- kern.ktrace.request_pool
- bounds the number of trace events being logged at a time.
Sysctl tunables that control process debuggability (as determined by
p_candebug(9)) also affect the operation of
ktrace
().
RETURN VALUES¶
The
ktrace
() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable
errno is set to indicate
the error.
ERRORS¶
The
ktrace
() system call will fail if:
- [
ENOTDIR
]
- A component of the path prefix is not a directory.
- [
ENAMETOOLONG
]
- A component of a pathname exceeded 255 characters, or an entire path name
exceeded 1023 characters.
- [
ENOENT
]
- The named tracefile does not exist.
- [
EACCES
]
- Search permission is denied for a component of the path prefix.
- [
ELOOP
]
- Too many symbolic links were encountered in translating the pathname.
- [
EIO
]
- An I/O error occurred while reading from or writing to the file
system.
- [
ENOSYS
]
- The kernel was not compiled with
ktrace
support.
A thread may be unable to log one or more tracing events due to a temporary
shortage of resources. This condition is remembered by the kernel, and the
next tracing request that succeeds will have the flag
KTR_DROP
set in its
ktr_type field.
SEE ALSO¶
kdump(1),
ktrace(1),
utrace(2),
sysctl(8),
p_candebug(9)
HISTORY¶
The
ktrace
() system call first appeared in
4.4BSD.