#top strace¶

Count time, calls, and errors for each system call and report a summary on program exit. On Linux, this attempts to show system time (CPU time spent running in the kernel) independent of wall clock time. If -c is used with -f or -F (below), only aggregate totals for all traced processes are kept.

Show some debugging output of strace itself on the standard error.

Trace child processes as they are created by currently traced processes as a result of the fork(2) system call.

On non-Linux platforms the new process is attached to as soon as its pid is known (through the return value of fork(2) in the parent process). This means that such children may run uncontrolled for a while (especially in the case of a vfork(2)), until the parent is scheduled again to complete its (v)fork(2) call. On Linux the child is traced from its first instruction with no delay. If the parent process decides to wait(2) for a child that is currently being traced, it is suspended until an appropriate child process either terminates or incurs a signal that would cause it to terminate (as determined from the child's current signal disposition).

On SunOS 4.x the tracing of vforks is accomplished with some dynamic linking trickery.

If the -o filename option is in effect, each processes trace is written to filename.pid where pid is the numeric process id of each process. This is incompatible with -c, since no per-process counts are kept.

This option is now obsolete and it has the same functionality as -f.

Print the help summary.

Print the instruction pointer at the time of the system call.

Suppress messages about attaching, detaching etc. This happens automatically when output is redirected to a file and the command is run directly instead of attaching.

Print a relative timestamp upon entry to each system call. This records the time difference between the beginning of successive system calls.

Prefix each line of the trace with the time of day.

If given twice, the time printed will include the microseconds.

If given thrice, the time printed will include the microseconds and the leading portion will be printed as the number of seconds since the epoch.

Show the time spent in system calls. This records the time difference between the beginning and the end of each system call.

Print unabbreviated versions of environment, stat, termios, etc. calls. These structures are very common in calls and so the default behavior displays a reasonable subset of structure members. Use this option to get all of the gory details.

Print the version number of strace.

Print all non-ASCII strings in hexadecimal string format.

Print all strings in hexadecimal string format.

Align return values in a specific column (default column 40).

A qualifying expression which modifies which events to trace or how to trace them. The format of the expression is:

[qualifier=][!]value1[,value2]...

where qualifier is one of trace, abbrev, verbose, raw, signal, read, or write and value is a qualifier-dependent symbol or number. The default qualifier is trace. Using an exclamation mark negates the set of values. For example, -eopen means literally -e trace=open which in turn means trace only the open system call. By contrast, -etrace=!open means to trace every system call except open. In addition, the special values all and none have the obvious meanings.

Note that some shells use the exclamation point for history expansion even inside quoted arguments. If so, you must escape the exclamation point with a backslash.

Trace only the specified set of system calls. The -c option is useful for determining which system calls might be useful to trace. For example, trace=open,close,read,write means to only trace those four system calls. Be careful when making inferences about the user/kernel boundary if only a subset of system calls are being monitored. The default is trace=all.

Trace all system calls which take a file name as an argument. You can think of this as an abbreviation for -e trace=open,stat,chmod,unlink,... which is useful to seeing what files the process is referencing. Furthermore, using the abbreviation will ensure that you don't accidentally forget to include a call like lstat in the list. Betchya woulda forgot that one.

Trace all system calls which involve process management. This is useful for watching the fork, wait, and exec steps of a process.

Trace all the network related system calls.

Trace all signal related system calls.

Trace all IPC related system calls.

Trace all file descriptor related system calls.

Abbreviate the output from printing each member of large structures. The default is abbrev=all. The -v option has the effect of abbrev=none.

Dereference structures for the specified set of system calls. The default is verbose=all.

Print raw, undecoded arguments for the specified set of system calls. This option has the effect of causing all arguments to be printed in hexadecimal. This is mostly useful if you don't trust the decoding or you need to know the actual numeric value of an argument.

Trace only the specified subset of signals. The default is signal=all. For example, signal=!SIGIO (or signal=!io) causes SIGIO signals not to be traced.

Perform a full hexadecimal and ASCII dump of all the data read from file descriptors listed in the specified set. For example, to see all input activity on file descriptors 3 and 5 use -e read=3,5. Note that this is independent from the normal tracing of the read(2) system call which is controlled by the option -e trace=read.

Perform a full hexadecimal and ASCII dump of all the data written to file descriptors listed in the specified set. For example, to see all output activity on file descriptors 3 and 5 use -e write=3,5. Note that this is independent from the normal tracing of the write(2) system call which is controlled by the option -e trace=write.

Write the trace output to the file filename rather than to stderr. Use filename.pid if -ff is used. If the argument begins with '|' or with '!' then the rest of the argument is treated as a command and all output is piped to it. This is convenient for piping the debugging output to a program without affecting the redirections of executed programs.

Set the overhead for tracing system calls to overhead microseconds. This is useful for overriding the default heuristic for guessing how much time is spent in mere measuring when timing system calls using the -c option. The accuracy of the heuristic can be gauged by timing a given program run without tracing (using time(1)) and comparing the accumulated system call time to the total produced using -c.

Attach to the process with the process ID pid and begin tracing. The trace may be terminated at any time by a keyboard interrupt signal (CTRL-C). strace will respond by detaching itself from the traced process(es) leaving it (them) to continue running. Multiple -p options can be used to attach to up to 32 processes in addition to command (which is optional if at least one -p option is given).

Specify the maximum string size to print (the default is 32). Note that filenames are not considered strings and are always printed in full.

Sort the output of the histogram printed by the -c option by the specified criterion. Legal values are time, calls, name, and nothing (default time).

Run command with the user ID, group ID, and supplementary groups of username. This option is only useful when running as root and enables the correct execution of setuid and/or setgid binaries. Unless this option is used setuid and setgid programs are executed without effective privileges.

Run command with var=val in its list of environment variables.

Remove var from the inherited list of environment variables before passing it on to the command.