linux - Linux 中的 "rm"命令如何工作？

Question

我想知道 rm 命令在 Linux 中是如何工作的。它调用了哪些系统调用？执行该命令使用了哪些文件操作？

抱歉，如果我的问题看起来微不足道，但我是 Linux 文件系统的新手。

Answer 1

strace(1) 应该很容易回答这样的问题:

$ touch test
$ strace rm test
execve("/usr/bin/rm", ["rm", "test"], [/* 26 vars */]) = 0
brk(0)                                  = 0xb86000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fabf8423000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=45618, ...}) = 0
mmap(NULL, 45618, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fabf8417000
close(3)                                = 0
open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\34\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=2107760, ...}) = 0
mmap(NULL, 3932736, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fabf7e42000
mprotect(0x7fabf7ff8000, 2097152, PROT_NONE) = 0
mmap(0x7fabf81f8000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b6000) = 0x7fabf81f8000
mmap(0x7fabf81fe000, 16960, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fabf81fe000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fabf8416000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fabf8414000
arch_prctl(ARCH_SET_FS, 0x7fabf8414740) = 0
mprotect(0x7fabf81f8000, 16384, PROT_READ) = 0
mprotect(0x60d000, 4096, PROT_READ)     = 0
mprotect(0x7fabf8424000, 4096, PROT_READ) = 0
munmap(0x7fabf8417000, 45618)           = 0
brk(0)                                  = 0xb86000
brk(0xba7000)                           = 0xba7000
brk(0)                                  = 0xba7000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=106065056, ...}) = 0
mmap(NULL, 106065056, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fabf191b000
close(3)                                = 0
open("/usr/share/locale/locale.alias", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=2502, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fabf8422000
read(3, "# Locale name alias data base.\n#"..., 4096) = 2502
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x7fabf8422000, 4096)            = 0
open("/usr/lib/locale/UTF-8/LC_CTYPE", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
newfstatat(AT_FDCWD, "test", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
geteuid()                               = 7026
newfstatat(AT_FDCWD, "test", {st_mode=S_IFREG|0664, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0
faccessat(AT_FDCWD, "test", W_OK)       = 0
unlinkat(AT_FDCWD, "test", 0)           = 0
lseek(0, 0, SEEK_CUR)                   = -1 ESPIPE (Illegal seek)
close(0)                                = 0
close(1)                                = 0
close(2)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++

在我的案例中，决定性的调用是 unlinkat(AT_FDCWD, "test", 0) 但具体情况可能取决于系统架构和 rm 版本。