User Commands truss(1)
NAME
truss - trace system calls and signals
SYNOPSIS
truss [-fcaeildDE] [- [tTvx] [!] syscall ,...]
[- [sS] [!] signal ,...] [- [mM] [!] fault ,...]
[- [rw] [!] fd ,...]
[- [uU] [!] lib ,... : [:] [!] func ,...]
[-o outfile] command | -p pid[/lwps]...
DESCRIPTION
The truss utility executes the specified command and pro-
duces a trace of the system calls it performs, the signals it receives, and the machine faults it incurs. Each line of the trace output reports either the fault or signal name or the system call name with its arguments and return value(s).System call arguments are displayed symbolically when possi-
ble using defines from relevant system headers. For any pathname pointer argument, the pointed-to string is displayed.
Error returns are reported using the error code namesdescribed in Intro(3). If, in the case of an error, the ker-
nel reports a missing privilege, a privilege name as described in privileges(5) is reported in square brackets ([ ]) after the error code name.Optionally (see the -u option), truss also produce an
entry/exit trace of user-level function calls executed by
the traced process, indented to indicate nesting. OPTIONS For those options that take a list argument, the name all can be used as a shorthand to specify all possible members of the list. If the list begins with a !, the meaning of the option is negated (for example, exclude rather than trace). Multiple occurrences of the same option can be specified. For the same name in a list, subsequent options (those to the right) override previous ones (those to the left). The following options are supported:-a
Shows the argument strings that are passed in each exec() system call.-c
Counts traced system calls, faults, and signals ratherSunOS 5.11 Last change: 31 Jul 2004 1
User Commands truss(1)
than displaying the trace line-by-line. A summary report
is produced after the traced command terminates or whentruss is interrupted. If -f is also specified, the
counts include all traced system calls, faults, and sig-
nals for child processes.-d
Includes a time stamp on each line of trace output. The time stamp appears as a field containing seconds.fraction at the start of the line. This represents a time in seconds relative to the beginning of the trace. The first line of the trace output shows the base time from which the individual time stamps are measured, both as seconds since the epoch (see time(2)) and as a date string (see ctime(3C) and date(1)). The times that are reported are the times that the event in question occurred. For all system calls, the event is the completion of the system call, not the start of the system call.-D
Includes a time delta on each line of trace output. The value appears as a field containing seconds.fraction and represents the elapsed time for the LWP that incurred the event since the last reported event incurred by that LWP. Specifically, for system calls, this is not the time spent within the system call.-e
Shows the environment strings that are passed in each exec() system call.-E
Includes a time delta on each line of trace output. The value appears as a field containing seconds.fraction and represents the difference in time elapsed between the beginning and end of a system call.In contrast to the -D option, this is the amount of
time spent within the system call.-f
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User Commands truss(1)
Follows all children created by fork() or vfork() and includes their signals, faults, and system calls in thetrace output. Normally, only the first-level command or
process is traced. When -f is specified, the process-id
is included with each line of trace output to indicate which process executed the system call or received the signal.-i
Does not display interruptible sleeping system calls.Certain system calls, such as open() and read() on ter-
minal devices or pipes, can sleep for indefinite periodsand are interruptible. Normally, truss reports such
sleeping system calls if they remain asleep for more than one second. The system call is reported again asecond time when it completes. The -i option causes such
system calls to be reported only once, when they com-
plete.-l
Includes the id of the responsible lightweight process(LWP) with each line of trace output. If -f is also
specified, both the process-id and the LWP-id are
included.-m [!]fault,...
Machine faults to trace or exclude. Those faults speci-
fied in the comma-separated list are traced. Faults can
be specified by name or number (see). If the list begins with a !, the specified faults are excluded from the trace output. Default is -mall -m
!fltpage.-M [!]fault,...
Machine faults that stop the process. The specifiedfaults are added to the set specified by -m. If one of
the specified faults is incurred, truss leaves the pro-
cess stopped and abandoned (see the -T option). Default
is -M!all.
-o outfile
File to be used for the trace output. By default, theSunOS 5.11 Last change: 31 Jul 2004 3
User Commands truss(1)
output goes to standard error.-p
Interprets the command arguments to truss as a list of
process-ids for existing processes (see ps(1)) rather
than as a command to be executed. truss takes control of
each process and begins tracing it provided that the userid and groupid of the process match those of the user or that the user is a privileged user. Users cantrace only selected threads by appending /thread-id to
the process-id. Mutiple threads can be selected using
the - and , delimiters. For example /1,2,7-9 traces
threads 1, 2, 7, 8, and 9. Processes can also be speci-
fied by their names in the /proc directory, for example, /proc/12345.-r [!]fd,...
Shows the full contents of the I/O buffer for each read() on any of the specified file descriptors. The output is formatted 32 bytes per line and shows each byte as an ASCII character (preceded by one blank) or as
a 2-character C language escape sequence for control
characters such as horizontal tab (\t) and newline (\n). If ASCII interpretation is not possible, the byte isshown in 2-character hexadecimal representation. (The
first 12 bytes of the I/O buffer for each traced print
>read() are shown even in the absence of -r.) Default is
-r!all.
-s [!]signal,...
Signals to trace or exclude. Those signals specified inthe comma-separated list are traced. The trace output
reports the receipt of each specified signal, even ifthe signal is being ignored (not blocked). (Blocked sig-
nals are not received until they are unblocked.) Signals can be specified by name or number (see). If the list begins with a !, the specified signals are excluded from the trace output. Default is -sall.
-S [!]signal,...
Signals that stop the process. The specified signals areadded to the set specified by -s. If one of the speci-
fied signals is received, truss leaves the process
stopped and abandoned (see the -T option). Default is
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User Commands truss(1)
-S!all.
-t [!]syscall,...
System calls to trace or exclude. Those system callsspecified in the comma-separated list are traced. If the
list begins with a !, the specified system calls areexcluded from the trace output. Default is -tall.
-T [!]syscall,...
Specifies system calls that stop the process. The speci-
fied system calls are added to the set specified by -t.
If one of the specified system calls is encountered,truss leaves the process stopped and abandoned. That is,
truss releases the process and exits but leaves the pro-
cess in the stopped state at completion of the system call in question. A debugger or other process inspection tool (see proc(1)) can then be applied to the stoppedprocess. truss can be reapplied to the stopped process
with the same or different options to continue tracing.Default is -T!all.
A process left stopped in this manner cannot be res-
tarted by the application of kill -CONT because it is
stopped on an event of interest via /proc, not by the default action of a stopping signal (see signal.h(3HEAD)). The prun(1) command described in proc(1) can be used to set the stopped process running again.-u [!]lib,...:[:][!]func,...
User-level function call tracing. lib,... is a comma-
separated list of dynamic library names, excluding the``.so.n'' suffix. func,... is a comma-separated list of
function names. In both cases the names can includename-matching metacharacters *,?,[] with the same mean-
ings as those of sh(1) but as applied to the library/function name spaces, not to files. An empty library or function list defaults to *, trace all libraries or functions in a library. A leading ! on either list specifies an exclusion list, names of libraries or functions not to be traced. Excluding a library excludes all functions in that library; any function list following a library exclusion list is ignored. A single : separating the library list from the functionSunOS 5.11 Last change: 31 Jul 2004 5
User Commands truss(1)
list means to trace calls into the libraries from out-
side the libraries, but omit calls made to functions in a library from other functions in the same library. Adouble :: means to trace all calls, regardless of ori-
gin. Library patterns do not match either the executable file or the dynamic linker unless there is an exact match (l* does not match ld.so.1). To trace functions in either of these objects, the names must be specified exactly, as in:truss -u a.out -u ld ...
a.out is the literal name to be used for this purpose; it does not stand for the name of the executable file. Tracing a.out function calls implies all calls (default is ::).Multiple -u options can be specified and they are
honored left-to-right. The id of the thread that per-
formed the function call is included in the trace outputfor the call. truss searches the dynamic symbol table in
each library to find function names and also searches the standard symbol table if it has not been stripped.-U [!]lib,...:[:][!]func,...
User-level function calls that stop the process. The
specified functions are added to the set specified by-u. If one of the specified functions is called, truss
leaves the process stopped and abandoned (see the -T
option).-v [!]syscall,...
Verbose. Displays the contents of any structures passed by address to the specified system calls (if traced by-t). Input values as well as values returned by the
operating system are shown. For any field used as both input and output, only the output value is shown.Default is -v!all.
-w [!]fd,...
Shows the contents of the I/O buffer for each write() on
any of the specified file descriptors (see the -r
option). Default is -w!all.
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User Commands truss(1)
-x [!]syscall,...
Displays the arguments to the specified system calls (iftraced by -t) in raw form, usually hexadecimal, rather
than symbolically. This is for unredeemed hackers whomust see the raw bits to be happy. Default is -x!all.
See man pages section 2: System Calls for system call namesaccepted by the -t, -T, -v, and -x options. System call
numbers are also accepted.If truss is used to initiate and trace a specified command
and if the -o option is used or if standard error is
redirected to a non-terminal file, then truss runs with
hangup, interrupt, and quit signals ignored. This facili-
tates tracing of interactive programs that catch interrupt and quit signals from the terminal. If the trace output remains directed to the terminal, or ifexisting processes are traced (the -p option), then truss
responds to hangup, interrupt, and quit signals by releasing all traced processes and exiting. This enables the user toterminate excessive trace output and to release previously-
existing processes. Released processes continue normally, as though they had never been touched.EXAMPLES
Example 1 Tracing a CommandThe following example produces a trace of the find(1) com-
mand on the terminal:example$ truss find . -print >find.out
Example 2 Tracing Common System Calls The following example shows only a trace of the open, close, read, and write system calls:example$ truss -t open,close,read,write find . -print >find.out
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User Commands truss(1)
Example 3 Tracing a Shell ScriptThe following example produces a trace of the spell(1) com-
mand on the file truss.out:
example$ truss -f -o truss.out spell document
spell is a shell script, so the -f flag is needed to trace
not only the shell but also the processes created by the shell. (The spell script runs a pipeline of eight processes.) Example 4 Abbreviating Output The following example abreviates output:example$ truss nroff -mm document >nroff.out
because 97% of the output reports lseek(), read(), and
write() system calls. To abbreviate it:example$ truss -t !lseek,read,write nroff -mm document >nroff.out
Example 5 Tracing Library Calls From Outside the C LibraryThe following example traces all user-level calls made to
any function in the C library from outside the C library:example$ truss -u libc ...
Example 6 Tracing library calls from within the C librarySunOS 5.11 Last change: 31 Jul 2004 8
User Commands truss(1)
The following example includes calls made to functions in the C library from within the C library itself:example$ truss -u libc:: ...
Example 7 Tracing Library Calls Other Than the C LibraryThe following example traces all user-level calls made to
any library other than the C library:example$ truss -u '*' -u !libc ...
Example 8 Tracing printf and scanf Function CallsThe following example traces all user-level calls to func-
tions in the printf and scanf family contained in the C library:example$ truss -u 'libc:*printf,*scanf' ...
Example 9 Tracing Every User-level Function Call
The following example traces every user-level function call
from anywhere to anywhere:example$ truss -u a.out -u ld:: -u :: ...
Example 10 Tracing a System Call Verbosely The following example verbosely traces the system callactivity of process #1, init(1M) (if you are a privileged
user):example# truss -p -v all 1
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User Commands truss(1)
Interrupting truss returns init to normal operation.
FILES /proc/* Process filesATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | developer/linker ||_____________________________|_____________________________|
SEE ALSO
date(1), find(1), proc(1), ps(1), sh(1), spell(1), init(1M), Intro(3), exec(2), fork(2), lseek(2), open(2), read(2), time(2), vfork(2), write(2), ctime(3C), signal.h(3HEAD), proc(4), attributes(5), privileges(5), threads(5) man pages section 2: System Calls NOTES Some of the system calls described in man pages section 2:System Calls differ from the actual operating system inter-
faces. Do not be surprised by minor deviations of the trace output from the descriptions in that document. Every machine fault (except a page fault) results in the posting of a signal to the LWP that incurred the fault. A report of a received signal immediately follows each report of a machine fault (except a page fault) unless that signal is being blocked. The operating system enforces certain security restrictions on the tracing of processes. In particular, any command whose object file (a.out) cannot be read by a user cannot betraced by that user; set-uid and set-gid commands can be
traced only by a privileged user. Unless it is run by aprivileged user, truss loses control of any process that
performs an exec() of a set-id or unreadable object file;
such processes continue normally, though independently oftruss, from the point of the exec().
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User Commands truss(1)
To avoid collisions with other controlling processes, truss
does not trace a process that it detects is being controlled by another process via the /proc interface. This allowstruss to be applied to proc(4)-based debuggers as well as to
another instance of itself.The trace output contains tab characters under the assump-
tion that standard tab stops are set (every eight posi-
tions).The trace output for multiple processes or for a mul-
tithreaded process (one that contains more than one LWP) is not produced in strict time order. For example, a read() on a pipe can be reported before the corresponding write(). For any one LWP (a traditional process contains only one), theoutput is strictly time-ordered.
When tracing more than one process, truss runs as one con-
trolling process for each process being traced. For the example of the spell command shown above, spell itself uses9 process slots, one for the shell and 8 for the 8-member
pipeline, while truss adds another 9 processes, for a total
of 18. Not all possible structures passed in all possible systemcalls are displayed under the -v option.
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