What do shared libraries do and why does ls need to load so many?

Question

I've been using strace on the ls command and I came across the large chunk of text below, and in doing a bit of research I've found that the vast majority of this is loading or reading shared libraries. My question is, in simple beginner terms, what are shared libraries and why does ls need so many if the final few lines completes all we need to do?

For context, I'm trying to explain what a simple process like ls does from being called upon to being terminated.

execve("/usr/bin/ls", ["ls"], 0x7ffeaa5999c0 /* 49 vars */) = 0
brk(NULL)                               = 0x5616fe4fa000
arch_prctl(0x3001 /* ARCH_??? */, 0x7ffc4fdc9040) = -1 EINVAL (Invalid argument)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=58140, ...}) = 0
mmap(NULL, 58140, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f25a2a11000
close(3)                                = 0
openat(AT_FDCWD, "/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@p\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=163200, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f25a2a0f000
mmap(NULL, 174600, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f25a29e4000
mprotect(0x7f25a29ea000, 135168, PROT_NONE) = 0
mmap(0x7f25a29ea000, 102400, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7f25a29ea000
mmap(0x7f25a2a03000, 28672, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1f000) = 0x7f25a2a03000 
mmap(0x7f25a2a0b000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x26000) = 0x7f25a2a0b000 
mmap(0x7f25a2a0d000, 6664, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f25a2a0d000
close(3)                                = 0
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/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\360A\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
pread64(3, "\4\0\0\0\20\0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0", 32, 848) = 32
pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\237\333t\347\262\27\320l\223\27*\202C\370T\177"..., 68, 880) = 68
fstat(3, {st_mode=S_IFREG|0755, st_size=2029560, ...}) = 0
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 784, 64) = 784
pread64(3, "\4\0\0\0\20\0\0\0\5\0\0\0GNU\0\2\0\0\300\4\0\0\0\3\0\0\0\0\0\0\0", 32, 848) = 32
pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\237\333t\347\262\27\320l\223\27*\202C\370T\177"..., 68, 880) = 68
mmap(NULL, 2037344, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f25a27f2000
mmap(0x7f25a2814000, 1540096, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x22000) = 0x7f25a2814000 
mmap(0x7f25a298c000, 319488, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x19a000) = 0x7f25a298c000 
mmap(0x7f25a29da000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1e7000) = 0x7f25a29da000 
mmap(0x7f25a29e0000, 13920, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f25a29e0000
close(3)                                = 0
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libpcre2-8.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\340\"\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=584392, ...}) = 0
mmap(NULL, 586536, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f25a2762000
mmap(0x7f25a2764000, 409600, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7f25a2764000 
mmap(0x7f25a27c8000, 163840, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x66000) = 0x7f25a27c8000 
mmap(0x7f25a27f0000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x8d000) = 0x7f25a27f0000 
close(3)                                = 0
openat(AT_FDCWD, "/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 \22\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=18816, ...}) = 0
mmap(NULL, 20752, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f25a275c000
mmap(0x7f25a275d000, 8192, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1000) = 0x7f25a275d000 
mmap(0x7f25a275f000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3000) = 0x7f25a275f000 
mmap(0x7f25a2760000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3000) = 0x7f25a2760000 
close(3)                                = 0
openat(AT_FDCWD, "/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\220q\0\0\0\0\0\0"..., 832) = 832
pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\360\2300%\360\340\363'\246\332u/\364\377\246u"..., 68, 824) = 68
fstat(3, {st_mode=S_IFREG|0755, st_size=157224, ...}) = 0
pread64(3, "\4\0\0\0\24\0\0\0\3\0\0\0GNU\0\360\2300%\360\340\363'\246\332u/\364\377\246u"..., 68, 824) = 68
mmap(NULL, 140408, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f25a2739000
mmap(0x7f25a273f000, 69632, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7f25a273f000 
mmap(0x7f25a2750000, 24576, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x17000) = 0x7f25a2750000 
mmap(0x7f25a2756000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c000) = 0x7f25a2756000 
mmap(0x7f25a2758000, 13432, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f25a2758000
close(3)                                = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f25a2737000
arch_prctl(ARCH_SET_FS, 0x7f25a2738400) = 0 mprotect(0x7f25a29da000, 16384, PROT_READ) = 0 mprotect(0x7f25a2756000, 4096, PROT_READ) = 0 
mprotect(0x7f25a2760000, 4096, PROT_READ) = 0 
mprotect(0x7f25a27f0000, 4096, PROT_READ) = 0 
mprotect(0x7f25a2a0b000, 4096, PROT_READ) = 0 mprotect(0x5616fca52000, 4096, PROT_READ) = 0 mprotect(0x7f25a2a4d000, 4096, PROT_READ) = 0
munmap(0x7f25a2a11000, 58140)           = 0 
set_tid_address(0x7f25a27386d0)         = 1376 
set_robust_list(0x7f25a27386e0, 24)     = 0
rt_sigaction(SIGRTMIN, {sa_handler=0x7f25a273fbf0, sa_mask=[], sa_flags=SA_RESTORER|SA_SIGINFO, sa_restorer=0x7f25a274d3c0}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {sa_handler=0x7f25a273fc90, sa_mask=[], sa_flags=SA_RESTORER|SA_RESTART|SA_SIGINFO, sa_restorer=0x7f25a274d3c0}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
statfs("/sys/fs/selinux", 0x7ffc4fdc8f90) = -1 ENOENT (No such file or directory)
statfs("/selinux", 0x7ffc4fdc8f90)      = -1 ENOENT (No such file or directory)
brk(NULL)                               = 0x5616fe4fa000 
brk(0x5616fe51b000)                     = 0x5616fe51b000 
openat(AT_FDCWD, "/proc/filesystems", O_RDONLY|O_CLOEXEC) = 3 
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
read(3, "nodev\tsysfs\nnodev\ttmpfs\nnodev\tbd"..., 1024) = 360 
read(3, "", 1024)                       = 0 close(3)                                = 0
access("/etc/selinux/config", F_OK)     = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=5699248, ...}) = 0
mmap(NULL, 5699248, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f25a21c7000 
close(3)                                = 0
ioctl(1, TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(1, TIOCGWINSZ, {ws_row=24, ws_col=80, ws_xpixel=0, ws_ypixel=0}) = 0
openat(AT_FDCWD, ".", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3 
fstat(3, {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
getdents64(3, /* 20 entries */, 32768)  = 624 getdents64(3, /* 0 entries */, 32768)   = 0
close(3)                                = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0), ...}) = 0 
write(1, "Desktop  Documents  Downloads  M"..., 72Desktop  Documents  Downloads  Music  Pictures    Public    Templates  Videos ) = 72 
close(1)                                = 0 close(2)                                = 0
exit_group(0)                           = ? +++ exited with 0 +++ 

Answer 1

in simple beginner terms, what are shared libraries

Shared libraries allow

1. binaries to share common code, so you don't store 1000+ separate instances of printf code on disk and in RAM, and
2. allow a bug fix to affect all binaries at once.

(1) used to be important when disks were 10MiB and 64KiB was a lot of RAM, but now this reason has diminished in importance.

The importance of (2) has dramatically increased -- with 1000s of binaries on a single system it's impractical to rebuild them all (which would be required for bug fix to take effect if not for shared libraries).

and why does ls need so many

It only uses few libraries: libc.so.6, libdl.so.2 and libpthread.so.0, libselinux.so.1 and libpcre2-8.so.0. For comparison, something like firefox or google-chrome use 90+, and some binaries I work with use 10,000+.

ls is not necessarily a simple program -- it can do color, it can display and sort file names in multiple locales, etc.