strace usage
Table of Contents
Example unlink VS rm
unlink
$ touch file1 $ strace -s 2000 -o unlink.log unlink file1
rm
$ touch file1 $ strace -s 2000 -o rm.log rm file1
With unlink it's invoking the unlink() system call:
... mmap(NULL, 7216688, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fb8fa621000 close(3) = 0 unlink("file1") = 0 close(1) = 0 close(2) = 0 exit_group(0) = ? ...
With rm it's a slightly different path:
... ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0 newfstatat(AT_FDCWD, "file1", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0 geteuid() = 1000 newfstatat(AT_FDCWD, "file1", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0 faccessat(AT_FDCWD, "file1", W_OK) = 0 unlinkat(AT_FDCWD, "file1", 0) = 0 lseek(0, 0, SEEK_CUR) = -1 ESPIPE (Illegal seek) close(0) = 0 close(1) = 0 close(2) = 0 exit_group(0) = ? ...
The system calls unlink() and unlinkat() are essentially the same
except for the differences described in this man page:
http://linux.die.net/man/2/unlinkat.
int unlinkat(int dirfd, const char *pathname, int flags);
The unlinkat() system call operates in exactly the same way as either
unlink(2) or rmdir(2) (depending on whether or not flags includes the
AT_REMOVEDIR flag) except for the differences described in this manual
page.
If the pathname given in pathname is relative, then it is interpreted
relative to the directory referred to by the file descriptor dirfd
(rather than relative to the current working directory of the calling
process, as is done by unlink(2) and rmdir(2) for a relative
pathname).
If the pathname given in pathname is relative and dirfd is the special
value AT_FDCWD, then pathname is interpreted relative to the current
working directory of the calling process (like unlink(2) and
rmdir(2)).
If the pathname given in pathname is absolute, then dirfd is ignored.