Which linux system call is used by ls command in linux to display the folder/file name?
Most of the system calls there are noise from loading shared libraries at startup. The interesting things happen here:
openat(AT_FDCWD, ".", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
getdents(3, /* 2 entries */, 32768) = 48
getdents(3, /* 0 entries */, 32768) = 0
close(3)
The openat(2)
system call is used to open the current directory ("."
) relative to the current working directory (the AT_FDCWD
flag). The O_DIRECTORY
flag indicates that it wants to open the directory and read the directory's contents.
The actual directory data is read using the getdents(2)
system call. In this case, it called it twice, since until it returns 0, it's not sure if there's more data or not. Finally, the file descriptor is closed after it's done.
If you were to write your own program, however, you wouldn't call these directly -- instead you'd use opendir(3)
, readdir(3)
, and closedir(3)
to read a directory. They're portable (POSIX-compliant), and they insulate you from the details of the underlying system calls. They're also easier to use, IMO.
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footy
Spending time in developing codes and new ideas. I also game a lot. Learning new technologies excite me!
Updated on September 03, 2020Comments
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footy almost 4 years
I wanted to know which system call is used in linux by the ls command to display the folder's (or file's name)? Especially the files/folders starting with "." (dot)
I executed the
strace ls -a
command to look at the system calls.There is a lot offstat
calls which occur for the all the other attributes (inode to permisisons). Which one actually gives it's name?execve("/bin/ls", ["ls", "-a"], [/* 37 vars */]) = 0 brk(0) = 0x1762000 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1c14025000 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=109464, ...}) = 0 mmap(NULL, 109464, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f1c1400a000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libselinux.so.1", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\20T\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0644, st_size=121936, ...}) = 0 mmap(NULL, 2221680, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f1c13be6000 mprotect(0x7f1c13c03000, 2093056, PROT_NONE) = 0 mmap(0x7f1c13e02000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c000) = 0x7f1c13e02000 mmap(0x7f1c13e04000, 1648, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f1c13e04000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/librt.so.1", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340!\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0644, st_size=31752, ...}) = 0 mmap(NULL, 2128984, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f1c139de000 mprotect(0x7f1c139e5000, 2093056, PROT_NONE) = 0 mmap(0x7f1c13be4000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7f1c13be4000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libacl.so.1", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\33\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0644, st_size=31096, ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1c14009000 mmap(NULL, 2126312, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f1c137d6000 mprotect(0x7f1c137dd000, 2093056, PROT_NONE) = 0 mmap(0x7f1c139dc000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7f1c139dc000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\200\30\2\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=1811128, ...}) = 0 mmap(NULL, 3925208, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f1c13417000 mprotect(0x7f1c135cc000, 2093056, PROT_NONE) = 0 mmap(0x7f1c137cb000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b4000) = 0x7f1c137cb000 mmap(0x7f1c137d1000, 17624, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f1c137d1000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libdl.so.2", O_RDONLY|O_CLOEXEC) = 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\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0644, st_size=14768, ...}) = 0 mmap(NULL, 2109704, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f1c13213000 mprotect(0x7f1c13215000, 2097152, PROT_NONE) = 0 mmap(0x7f1c13415000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7f1c13415000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\200l\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=135366, ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1c14008000 mmap(NULL, 2212904, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f1c12ff6000 mprotect(0x7f1c1300e000, 2093056, PROT_NONE) = 0 mmap(0x7f1c1320d000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x17000) = 0x7f1c1320d000 mmap(0x7f1c1320f000, 13352, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f1c1320f000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libattr.so.1", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340\17\0\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0644, st_size=18552, ...}) = 0 mmap(NULL, 2113736, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f1c12df1000 mprotect(0x7f1c12df5000, 2093056, PROT_NONE) = 0 mmap(0x7f1c12ff4000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3000) = 0x7f1c12ff4000 close(3) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1c14007000 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1c14005000 arch_prctl(ARCH_SET_FS, 0x7f1c140057c0) = 0 mprotect(0x7f1c137cb000, 16384, PROT_READ) = 0 mprotect(0x7f1c12ff4000, 4096, PROT_READ) = 0 mprotect(0x7f1c1320d000, 4096, PROT_READ) = 0 mprotect(0x7f1c13415000, 4096, PROT_READ) = 0 mprotect(0x7f1c139dc000, 4096, PROT_READ) = 0 mprotect(0x7f1c13be4000, 4096, PROT_READ) = 0 mprotect(0x7f1c13e02000, 4096, PROT_READ) = 0 mprotect(0x618000, 4096, PROT_READ) = 0 mprotect(0x7f1c14027000, 4096, PROT_READ) = 0 munmap(0x7f1c1400a000, 109464) = 0 set_tid_address(0x7f1c14005a90) = 4490 set_robust_list(0x7f1c14005aa0, 0x18) = 0 futex(0x7fff2e09d99c, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 1, NULL, 7f1c140057c0) = -1 EAGAIN (Resource temporarily unavailable) rt_sigaction(SIGRTMIN, {0x7f1c12ffc750, [], SA_RESTORER|SA_SIGINFO, 0x7f1c13005cb0}, NULL, 8) = 0 rt_sigaction(SIGRT_1, {0x7f1c12ffc7e0, [], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x7f1c13005cb0}, NULL, 8) = 0 rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0 getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0 statfs("/selinux", {f_type="EXT2_SUPER_MAGIC", f_bsize=4096, f_blocks=238304997, f_bfree=232078639, f_bavail=219973436, f_files=60530688, f_ffree=60120220, f_fsid={-1173666966, -474985328}, f_namelen=255, f_frsize=4096}) = 0 brk(0) = 0x1762000 brk(0x1783000) = 0x1783000 open("/proc/filesystems", O_RDONLY) = 3 fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1c14024000 read(3, "nodev\tsysfs\nnodev\trootfs\nnodev\tb"..., 1024) = 328 read(3, "", 1024) = 0 close(3) = 0 munmap(0x7f1c14024000, 4096) = 0 open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=7220736, ...}) = 0 mmap(NULL, 7220736, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f1c1270e000 close(3) = 0 ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0 ioctl(1, TIOCGWINSZ, {ws_row=41, ws_col=144, ws_xpixel=0, ws_ypixel=0}) = 0 openat(AT_FDCWD, ".", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3 getdents(3, /* 2 entries */, 32768) = 48 getdents(3, /* 0 entries */, 32768) = 0 close(3) = 0 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0 mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f1c14024000 write(1, ". ..\n", 6. .. ) = 6 close(1) = 0 munmap(0x7f1c14024000, 4096) = 0 close(2) = 0 exit_group(0) = ?