strace
2. -e 옵션을 사용해 특정 system call 트레이스
3. -o 옵션을 사용해 트레이스 내용을 파일로 저장하기
4. -p 옵션을 사용해 특정 프로세스를 선택해서 트레이스하기
5. -t 옵션을 사용해 트레이스 Output 결과라인에 Timestamp 찍기
6. -r 옵션을 사용해 output 라인마다 시간 간격을 표시해 줄 수 있다.
7. -c 옵션을 사용해 system call 에 대한 사용 통계 정보를 확인할 수 있다.
8. -T 옵션을 사용해 call 당 걸린 시간을 확인하여 오래걸리는 call 정보를 확인할 수 있다.
SunOS의 trace, strace, truss 와 유사한 진단, 디버깅 유틸이다.
리눅스 커널이나 프로세스간의 작용에 대한 내용을 모니터할 수 있다.
즉, system call, signal 전달과정, 프로세스 상태 변화등을 관찰할 수 있다.
유사 유틸
Linux : ltrace, xtrace, SystemTap, trace-cmd, KernelShark, ftrace
AIX : truss
HP-UX : Tusc
Solaris : truss, DTrace
UnixWare : truss
FreeBSD : truss, ktrace, DTrace
NetBSD : ktrace, DTrace
OpenBSD : ktrace, kdump
Mac OS X : ktrace, DTrace, dtruss
MS Windows : StraceNT, Process Monitor
아래 사용에 관한 7가지 예를 살펴보도록 하겠다.
1. 명령어 실행을 트레이스 하기
ls 명령어에 대한 트레이스를 하도록 해 보겠다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace ls
execve("/bin/ls", ["ls"], [/* 35 vars */]) = 0
brk(0) = 0x1c1b000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7ff5c2d4b000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=46959, ...}) = 0
mmap(NULL, 46959, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7ff5c2d3f000
close(3) = 0
open("/lib64/libselinux.so.1", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320X\300\3701\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=124624, ...}) = 0
mmap(0x31f8c00000, 2221912, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x31f8c00000
mprotect(0x31f8c1d000, 2093056, PROT_NONE) = 0
mmap(0x31f8e1c000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c000) = 0x31f8e1c000
mmap(0x31f8e1e000, 1880, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x31f8e1e000
close(3) = 0
open("/lib64/librt.so.1", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@!\300\3671\0\0\0"..., 832) = 832
.
.
.
2. -e 옵션을 사용해 특정 system call 트레이스
ls 명령어에서 사용한 open이라는 system call 만 트레이스
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -e open ls
open("/etc/ld.so.cache", O_RDONLY) = 3
open("/lib64/libselinux.so.1", O_RDONLY) = 3
open("/lib64/librt.so.1", O_RDONLY) = 3
open("/lib64/libcap.so.2", O_RDONLY) = 3
open("/lib64/libacl.so.1", O_RDONLY) = 3
open("/lib64/libc.so.6", O_RDONLY) = 3
open("/lib64/libdl.so.2", O_RDONLY) = 3
open("/lib64/libpthread.so.0", O_RDONLY) = 3
open("/lib64/libattr.so.1", O_RDONLY) = 3
open("/usr/lib/locale/locale-archive", O_RDONLY) = 3
open(".", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
1.sql login.sql
+++ exited with 0 +++
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL>
만약 여러개의 system call을 트레이스 하고 싶다면 "-e trace=" 옵션을 사용하면 된다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -e trace=open,read ls
open("/etc/ld.so.cache", O_RDONLY) = 3
open("/lib64/libselinux.so.1", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320X\300\3701\0\0\0"..., 832) = 832
open("/lib64/librt.so.1", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@!\300\3671\0\0\0"..., 832) = 832
open("/lib64/libcap.so.2", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0000\23@\3731\0\0\0"..., 832) = 832
open("/lib64/libacl.so.1", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\200\36@\0022\0\0\0"..., 832) = 832
open("/lib64/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\1\3671\0\0\0"..., 832) = 832
open("/lib64/libdl.so.2", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340\r\200\3671\0\0\0"..., 832) = 832
open("/lib64/libpthread.so.0", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340]@\3671\0\0\0"..., 832) = 832
open("/lib64/libattr.so.1", O_RDONLY) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\200\23\0\0052\0\0\0"..., 832) = 832
open("/usr/lib/locale/locale-archive", O_RDONLY) = 3
open(".", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
1.sql login.sql
+++ exited with 0 +++
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL>
3. -o 옵션을 사용해 트레이스 내용을 파일로 저장하기
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -o output.txt ls 1.sql login.sql output.txt testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> ls -alrt
4. -p 옵션을 사용해 특정 프로세스를 선택해서 트레이스하기
프로세스 pid를 통해 트레이스할 수 잇다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -p 20495 -o ora_cssdagent.txt Process 20495 attached ^CProcess 20495 detached testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL>
아래는 위 과정을 통해 얻게된 트레이스 파일을 tail 명령어를 통해 모니터링하는 내용이다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> tail -100f ora_cssdagent.txt times(NULL) = 553785768 times(NULL) = 553785768 futex(0x117b8c0, FUTEX_WAKE_PRIVATE, 1) = 1 times(NULL) = 553785768 futex(0x1189ba4, FUTEX_CMP_REQUEUE_PRIVATE, 1, 2147483647, 0x1189ad0, 360190) = 1 futex(0x1189ad0, FUTEX_WAKE_PRIVATE, 1) = 1 times(NULL) = 553785768 times(NULL) = 553785768 times(NULL) = 553785768 futex(0x1189ba4, FUTEX_CMP_REQUEUE_PRIVATE, 1, 2147483647, 0x1189ad0, 360192) = 1 futex(0x1189ad0, FUTEX_WAKE_PRIVATE, 1) = 1 times(NULL) = 553785768 times(NULL) = 553785768 futex(0x118ab64, FUTEX_CMP_REQUEUE_PRIVATE, 1, 2147483647, 0x118aa90, 545372) = 2 futex(0x118aa90, FUTEX_WAKE_PRIVATE, 1) = 1 times(NULL) = 553785768 times(NULL) = 553785768 futex(0x118ab64, FUTEX_CMP_REQUEUE_PRIVATE, 1, 2147483647, 0x118aa90, 545376) = 2 futex(0x118aa90, FUTEX_WAKE_PRIVATE, 1) = 1 futex(0x117b994, FUTEX_WAIT_PRIVATE, 505627, NULL) = 0 times(NULL) = 553788767 . . .
5. -t 옵션을 사용해 트레이스 Output 결과라인에 Timestamp 찍기
-t 옵션을 사용해 output 결과 라인마다 timestamp를 찍을 수 있다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -t -e open ls
21:06:03 open("/etc/ld.so.cache", O_RDONLY) = 3
21:06:03 open("/lib64/libselinux.so.1", O_RDONLY) = 3
21:06:03 open("/lib64/librt.so.1", O_RDONLY) = 3
21:06:03 open("/lib64/libcap.so.2", O_RDONLY) = 3
21:06:03 open("/lib64/libacl.so.1", O_RDONLY) = 3
21:06:03 open("/lib64/libc.so.6", O_RDONLY) = 3
21:06:03 open("/lib64/libdl.so.2", O_RDONLY) = 3
21:06:03 open("/lib64/libpthread.so.0", O_RDONLY) = 3
21:06:03 open("/lib64/libattr.so.1", O_RDONLY) = 3
21:06:03 open("/usr/lib/locale/locale-archive", O_RDONLY) = 3
21:06:03 open(".", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
1.sql login.sql ora_cssdagent.txt output.txt strace
21:06:03 +++ exited with 0 +++
-tt 옵션을 사용해 microsecond 수준으로 timestamp를 찍을 수도 있다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -tt -e open ls
14:54:29.466429 open("/etc/ld.so.cache", O_RDONLY) = 3
14:54:29.466799 open("/lib64/libselinux.so.1", O_RDONLY) = 3
14:54:29.467196 open("/lib64/librt.so.1", O_RDONLY) = 3
14:54:29.467570 open("/lib64/libcap.so.2", O_RDONLY) = 3
14:54:29.468202 open("/lib64/libacl.so.1", O_RDONLY) = 3
14:54:29.468638 open("/lib64/libc.so.6", O_RDONLY) = 3
14:54:29.469039 open("/lib64/libdl.so.2", O_RDONLY) = 3
14:54:29.469554 open("/lib64/libpthread.so.0", O_RDONLY) = 3
14:54:29.469971 open("/lib64/libattr.so.1", O_RDONLY) = 3
14:54:29.471870 open("/usr/lib/locale/locale-archive", O_RDONLY) = 3
14:54:29.472267 open(".", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
1.sql login.sql ora_cssdagent.txt output.txt
14:54:29.473038 +++ exited with 0 +++
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL>
6. -r 옵션을 사용해 output 라인마다 시간 간격을 표시해 줄 수 있다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -r ls
0.000000 execve("/bin/ls", ["ls"], [/* 35 vars */]) = 0
0.000560 brk(0) = 0x214d000
0.000105 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f8c998f7000
0.000096 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
0.000116 open("/etc/ld.so.cache", O_RDONLY) = 3
0.000078 fstat(3, {st_mode=S_IFREG|0644, st_size=46959, ...}) = 0
0.000068 mmap(NULL, 46959, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f8c998eb000
0.000070 close(3) = 0
0.000070 open("/lib64/libselinux.so.1", O_RDONLY) = 3
0.000067 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320X\300\3701\0\0\0"..., 832) = 832
0.000066 fstat(3, {st_mode=S_IFREG|0755, st_size=124624, ...}) = 0
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7. -c 옵션을 사용해 system call 에 대한 사용 통계 정보를 확인할 수 있다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -c ls 1.sql login.sql ora_cssdagent.txt output.txt % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 100.00 0.000026 1 27 mmap 0.00 0.000000 0 8 read 0.00 0.000000 0 1 write 0.00 0.000000 0 11 open 0.00 0.000000 0 13 close 0.00 0.000000 0 1 stat 0.00 0.000000 0 11 fstat 0.00 0.000000 0 16 mprotect 0.00 0.000000 0 2 munmap 0.00 0.000000 0 3 brk 0.00 0.000000 0 2 rt_sigaction 0.00 0.000000 0 1 rt_sigprocmask 0.00 0.000000 0 2 ioctl 0.00 0.000000 0 1 1 access 0.00 0.000000 0 1 execve 0.00 0.000000 0 1 fcntl 0.00 0.000000 0 2 getdents 0.00 0.000000 0 1 getrlimit 0.00 0.000000 0 2 statfs 0.00 0.000000 0 1 arch_prctl 0.00 0.000000 0 2 1 futex 0.00 0.000000 0 1 set_tid_address 0.00 0.000000 0 1 set_robust_list ------ ----------- ----------- --------- --------- ---------------- 100.00 0.000026 111 2 total testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL>
8. -T 옵션을 사용해 call 당 걸린 시간을 확인하여 오래걸리는 call 정보를 확인할 수 있다.
testora.localdomain@oracle:testdb:/home/oracle/DBA/script/SQL> strace -T ls
execve("/bin/ls", ["ls"], [/* 35 vars */]) = 0 <0.000352>
brk(0) = 0x1b52000 <0.000023>
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fd8f95e4000 <0.000027>
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory) <0.000030>
open("/etc/ld.so.cache", O_RDONLY) = 3 <0.000031>
fstat(3, {st_mode=S_IFREG|0644, st_size=46959, ...}) = 0 <0.000021>
mmap(NULL, 46959, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fd8f95d8000 <0.000025>
close(3) = 0 <0.000021>
open("/lib64/libselinux.so.1", O_RDONLY) = 3 <0.000029>
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320X\300\3701\0\0\0"..., 832) = 832 <0.000023>
.
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※ strace의 man page
NAME
strace - trace system calls and signals
SYNOPSIS
strace [-CdffhiqrtttTvVxxy] [-In] [-bexecve] [-eexpr]... [-acolumn] [-ofile] [-sstrsize] [-Ppath]... -ppid...
/ [-D] [-Evar[=val]]... [-uusername] command [args]
strace -c[df] [-In] [-bexecve] [-eexpr]... [-Ooverhead] [-Ssortby] -ppid... / [-D] [-Evar[=val]]... [-uuser-
name] command [args]
DESCRIPTION
In the simplest case strace runs the specified command until it exits. It intercepts and records the system
calls which are called by a process and the signals which are received by a process. The name of each system
call, its arguments and its return value are printed on standard error or to the file specified with the -o
option.
strace is a useful diagnostic, instructional, and debugging tool. System administrators, diagnosticians and
trouble-shooters will find it invaluable for solving problems with programs for which the source is not readily
available since they do not need to be recompiled in order to trace them. Students, hackers and the overly-
curious will find that a great deal can be learned about a system and its system calls by tracing even ordinary
programs. And programmers will find that since system calls and signals are events that happen at the
user/kernel interface, a close examination of this boundary is very useful for bug isolation, sanity checking
and attempting to capture race conditions.
Each line in the trace contains the system call name, followed by its arguments in parentheses and its return
value. An example from stracing the command ‘‘cat /dev/null’’ is:
open("/dev/null", O_RDONLY) = 3
Errors (typically a return value of -1) have the errno symbol and error string appended.
open("/foo/bar", O_RDONLY) = -1 ENOENT (No such file or directory)
Signals are printed as a signal symbol and a signal string. An excerpt from stracing and interrupting the com-
mand ‘‘sleep 666’’ is:
sigsuspend([] <unfinished ...>
--- SIGINT (Interrupt) ---
+++ killed by SIGINT +++
If a system call is being executed and meanwhile another one is being called from a different thread/process
then strace will try to preserve the order of those events and mark the ongoing call as being unfinished. When
the call returns it will be marked as resumed.
[pid 28772] select(4, [3], NULL, NULL, NULL <unfinished ...>
[pid 28779] clock_gettime(CLOCK_REALTIME, {1130322148, 939977000}) = 0
[pid 28772] <... select resumed> ) = 1 (in [3])
Interruption of a (restartable) system call by a signal delivery is processed differently as kernel terminates
the system call and also arranges its immediate reexecution after the signal handler completes.
read(0, 0x7ffff72cf5cf, 1) = ? ERESTARTSYS (To be restarted)
--- SIGALRM (Alarm clock) @ 0 (0) ---
rt_sigreturn(0xe) = 0
read(0, ""..., 1) = 0
Arguments are printed in symbolic form with a passion. This example shows the shell performing ‘‘>>xyzzy’’
output redirection:
open("xyzzy", O_WRONLY|O_APPEND|O_CREAT, 0666) = 3
Here the third argument of open is decoded by breaking down the flag argument into its three bitwise-OR con-
stituents and printing the mode value in octal by tradition. Where traditional or native usage differs from
ANSI or POSIX, the latter forms are preferred. In some cases, strace output has proven to be more readable
than the source.
Structure pointers are dereferenced and the members are displayed as appropriate. In all cases arguments are
formatted in the most C-like fashion possible. For example, the essence of the command ‘‘ls -l /dev/null’’ is
captured as:
lstat("/dev/null", {st_mode=S_IFCHR|0666, st_rdev=makedev(1, 3), ...}) = 0
Notice how the ‘struct stat’ argument is dereferenced and how each member is displayed symbolically. In par-
ticular, observe how the st_mode member is carefully decoded into a bitwise-OR of symbolic and numeric values.
Also notice in this example that the first argument to lstat is an input to the system call and the second
argument is an output. Since output arguments are not modified if the system call fails, arguments may not
always be dereferenced. For example, retrying the ‘‘ls -l’’ example with a non-existent file produces the fol-
lowing line:
lstat("/foo/bar", 0xb004) = -1 ENOENT (No such file or directory)
In this case the porch light is on but nobody is home.
Character pointers are dereferenced and printed as C strings. Non-printing characters in strings are normally
represented by ordinary C escape codes. Only the first strsize (32 by default) bytes of strings are printed;
longer strings have an ellipsis appended following the closing quote. Here is a line from ‘‘ls -l’’ where the
getpwuid library routine is reading the password file:
read(3, "root::0:0:System Administrator:/"..., 1024) = 422
While structures are annotated using curly braces, simple pointers and arrays are printed using square brackets
with commas separating elements. Here is an example from the command ‘‘id’’ on a system with supplementary
group ids:
getgroups(32, [100, 0]) = 2
On the other hand, bit-sets are also shown using square brackets but set elements are separated only by a
space. Here is the shell preparing to execute an external command:
sigprocmask(SIG_BLOCK, [CHLD TTOU], []) = 0
Here the second argument is a bit-set of two signals, SIGCHLD and SIGTTOU. In some cases the bit-set is so
full that printing out the unset elements is more valuable. In that case, the bit-set is prefixed by a tilde
like this:
sigprocmask(SIG_UNBLOCK, ~[], NULL) = 0
Here the second argument represents the full set of all signals.
OPTIONS
-c 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.
-C Like -c but also print regular output while processes are running.
-D Run tracer process as a detached grandchild, not as parent of the tracee. This reduces the
visible effect of strace by keeping the tracee a direct child of the calling process.
-d Show some debugging output of strace itself on the standard error.
-f Trace child processes as they are created by currently traced processes as a result of the
fork(2), vfork(2) and clone(2) system calls. Note that -p PID -f will attach all threads of
process PID if it is multi-threaded, not only thread with thread_id = PID.
-ff 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.
-F This option is now obsolete and it has the same functionality as -f.
-h Print the help summary.
-i Print the instruction pointer at the time of the system call.
-q 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.
-qq If given twice, suppress messages about process exit status.
-r Print a relative timestamp upon entry to each system call. This records the time difference
between the beginning of successive system calls.
-t Prefix each line of the trace with the time of day.
-tt If given twice, the time printed will include the microseconds.
-ttt 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.
-T Show the time spent in system calls. This records the time difference between the beginning
and the end of each system call.
-v 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 struc-
ture members. Use this option to get all of the gory details.
-V Print the version number of strace.
-x Print all non-ASCII strings in hexadecimal string format.
-xx Print all strings in hexadecimal string format.
-y Print paths associated with file descriptor arguments.
-a column Align return values in a specific column (default column 40).
-b syscall If specified syscall is reached, detach from traced process. Currently, only execve syscall
is supported. This option is useful if you want to trace multi-threaded process and there-
fore require -f, but don’t want to trace its (potentially very complex) children.
-e expr A qualifying expression which modifies which events to trace or how to trace them. The for-
mat 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, -e open means literally -e trace=open which in
turn means trace only the open system call. By contrast, -e trace=!open means to trace
every system call except open. In addition, the special values all and none have the obvi-
ous 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.
-e trace=set
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.
-e trace=file
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.
-e trace=process
Trace all system calls which involve process management. This is useful for watching the
fork, wait, and exec steps of a process.
-e trace=network
Trace all the network related system calls.
-e trace=signal
Trace all signal related system calls.
-e trace=ipc
Trace all IPC related system calls.
-e trace=desc
Trace all file descriptor related system calls.
-e trace=memory
Trace all memory mapping related system calls.
-e abbrev=set
Abbreviate the output from printing each member of large structures. The default is
abbrev=all. The -v option has the effect of abbrev=none.
-e verbose=set
Dereference structures for the specified set of system calls. The default is verbose=all.
-e raw=set 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.
-e signal=set
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.
-e read=set 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) sys-
tem call which is controlled by the option -e trace=read.
-e write=set
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.
-I interruptible
When strace can be interrupted by signals (such as pressing ^C). 1: no signals are blocked;
2: fatal signals are blocked while decoding syscall (default); 3: fatal signals are always
blocked (default if ’-o FILE PROG’); 4: fatal signals and SIGTSTP (^Z) are always blocked
(useful to make strace -o FILE PROG not stop on ^Z).
-o filename 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.
-O overhead 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.
-p pid Attach to the process with the process ID pid and begin tracing. The trace may be termi-
nated 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 many processes. -p "‘pidof PROG‘" syntax is supported.
-P path Trace only system calls accessing path. Multiple -P options can be used to specify several
paths.
-s strsize Specify the maximum string size to print (the default is 32). Note that filenames are not
considered strings and are always printed in full.
-S sortby Sort the output of the histogram printed by the -c option by the specified criterion. Legal
values are time, calls, name, and nothing (default is time).
-u username 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 set-
gid binaries. Unless this option is used setuid and setgid programs are executed without
effective privileges.
-E var=val Run command with var=val in its list of environment variables.
-E var Remove var from the inherited list of environment variables before passing it on to the com-
mand.
DIAGNOSTICS
When command exits, strace exits with the same exit status. If command is terminated by a signal,
strace terminates itself with the same signal, so that strace can be used as a wrapper process transpar-
ent to the invoking parent process.
When using -p, the exit status of strace is zero unless there was an unexpected error in doing the trac-
ing.
SETUID INSTALLATION
If strace is installed setuid to root then the invoking user will be able to attach to and trace pro-
cesses owned by any user. In addition setuid and setgid programs will be executed and traced with the
correct effective privileges. Since only users trusted with full root privileges should be allowed to
do these things, it only makes sense to install strace as setuid to root when the users who can execute
it are restricted to those users who have this trust. For example, it makes sense to install a special
version of strace with mode ‘rwsr-xr--’, user root and group trace, where members of the trace group are
trusted users. If you do use this feature, please remember to install a non-setuid version of strace
for ordinary lusers to use.
SEE ALSO
ltrace(1), time(1), ptrace(2), proc(5)
NOTES
It is a pity that so much tracing clutter is produced by systems employing shared libraries.
It is instructive to think about system call inputs and outputs as data-flow across the user/kernel
boundary. Because user-space and kernel-space are separate and address-protected, it is sometimes pos-
sible to make deductive inferences about process behavior using inputs and outputs as propositions.
In some cases, a system call will differ from the documented behavior or have a different name. For
example, on System V-derived systems the true time(2) system call does not take an argument and the stat
function is called xstat and takes an extra leading argument. These discrepancies are normal but
idiosyncratic characteristics of the system call interface and are accounted for by C library wrapper
functions.
On some platforms a process that has a system call trace applied to it with the -p option will receive a
SIGSTOP. This signal may interrupt a system call that is not restartable. This may have an unpre-
dictable effect on the process if the process takes no action to restart the system call.
BUGS
Programs that use the setuid bit do not have effective user ID privileges while being traced.
A traced process runs slowly.
Traced processes which are descended from command may be left running after an interrupt signal (CTRL-
C).
The -i option is weakly supported.
HISTORY
strace The original strace was written by Paul Kranenburg for SunOS and was inspired by its trace util-
ity. The SunOS version of strace was ported to Linux and enhanced by Branko Lankester, who also wrote
the Linux kernel support. Even though Paul released strace 2.5 in 1992, Branko’s work was based on
Paul’s strace 1.5 release from 1991. In 1993, Rick Sladkey merged strace 2.5 for SunOS and the second
release of strace for Linux, added many of the features of truss(1) from SVR4, and produced an strace
that worked on both platforms. In 1994 Rick ported strace to SVR4 and Solaris and wrote the automatic
configuration support. In 1995 he ported strace to Irix and tired of writing about himself in the third
person.
PROBLEMS
Problems with strace should be reported to the strace mailing list at <strace-devel@lists.source-
forge.net>.
2010-03-30 STRACE(1)
출처
http://www.thegeekstuff.com/2011/11/strace-examples/
https://ko.wikipedia.org/wiki/Strace
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