diff --git a/src/header/unistd/brk.rs b/src/header/unistd/brk.rs
index 47907758cf..73e7029040 100644
--- a/src/header/unistd/brk.rs
+++ b/src/header/unistd/brk.rs
@@ -8,6 +8,12 @@ use crate::{
 
 static mut BRK: *mut c_void = ptr::null_mut();
 
+/// See <https://pubs.opengroup.org/onlinepubs/7908799/xsh/brk.html>.
+///
+/// # Deprecation
+/// The `brk()` function was marked legacy in the System Interface & Headers
+/// Issue 5, and removed in Issue 6.
+#[deprecated]
 #[no_mangle]
 pub unsafe extern "C" fn brk(addr: *mut c_void) -> c_int {
     BRK = Sys::brk(addr).or_errno_null_mut();
@@ -20,6 +26,12 @@ pub unsafe extern "C" fn brk(addr: *mut c_void) -> c_int {
     0
 }
 
+/// See <https://pubs.opengroup.org/onlinepubs/7908799/xsh/brk.html>.
+///
+/// # Deprecation
+/// The `sbrk()` function was marked legacy in the System Interface & Headers
+/// Issue 5, and removed in Issue 6.
+#[deprecated]
 #[no_mangle]
 pub unsafe extern "C" fn sbrk(incr: intptr_t) -> *mut c_void {
     if BRK.is_null() {
diff --git a/src/header/unistd/getopt.rs b/src/header/unistd/getopt.rs
index e0b82c569f..5a3f28378c 100644
--- a/src/header/unistd/getopt.rs
+++ b/src/header/unistd/getopt.rs
@@ -4,26 +4,31 @@ use core::ptr;
 
 use crate::{header::getopt, platform::types::*};
 
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/getopt.html>.
 #[allow(non_upper_case_globals)]
 #[no_mangle]
 #[linkage = "weak"] // often redefined in GNU programs
 pub static mut optarg: *mut c_char = ptr::null_mut();
 
-#[allow(non_upper_case_globals)]
-#[no_mangle]
-#[linkage = "weak"] // often redefined in GNU programs
-pub static mut optind: c_int = 1;
-
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/getopt.html>.
 #[allow(non_upper_case_globals)]
 #[no_mangle]
 #[linkage = "weak"] // often redefined in GNU programs
 pub static mut opterr: c_int = 1;
 
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/getopt.html>.
+#[allow(non_upper_case_globals)]
+#[no_mangle]
+#[linkage = "weak"] // often redefined in GNU programs
+pub static mut optind: c_int = 1;
+
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/getopt.html>.
 #[allow(non_upper_case_globals)]
 #[no_mangle]
 #[linkage = "weak"] // often redefined in GNU programs
 pub static mut optopt: c_int = -1;
 
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/getopt.html>.
 #[no_mangle]
 #[linkage = "weak"] // often redefined in GNU programs
 pub unsafe extern "C" fn getopt(
diff --git a/src/header/unistd/getpass.rs b/src/header/unistd/getpass.rs
index 6776cad85b..0385cc71bb 100644
--- a/src/header/unistd/getpass.rs
+++ b/src/header/unistd/getpass.rs
@@ -60,6 +60,12 @@ fn getpass_rs(prompt: CStr, passbuff: &mut [u8]) -> Result<*mut c_char, io::Erro
     Ok(passbuff.as_mut_ptr() as *mut c_char)
 }
 
+/// See <https://pubs.opengroup.org/onlinepubs/7908799/xsh/getpass.html>.
+///
+/// # Deprecation
+/// The `getpass()` function was marked legacy in the Open Group System
+/// Interface & Headers Issue 5, and removed in Issue 6.
+#[deprecated]
 #[no_mangle]
 pub unsafe extern "C" fn getpass(prompt: *const c_char) -> *mut c_char {
     static mut PASSBUFF: [u8; PASS_MAX] = [0; PASS_MAX];
diff --git a/src/header/unistd/pathconf.rs b/src/header/unistd/pathconf.rs
index 074b65092f..0d81dade9c 100644
--- a/src/header/unistd/pathconf.rs
+++ b/src/header/unistd/pathconf.rs
@@ -56,11 +56,13 @@ fn pc(name: c_int) -> c_long {
     }
 }
 
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/fpathconf.html>.
 #[no_mangle]
 pub extern "C" fn fpathconf(_fildes: c_int, name: c_int) -> c_long {
     pc(name)
 }
 
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/fpathconf.html>.
 #[no_mangle]
 pub extern "C" fn pathconf(_path: *const c_char, name: c_int) -> c_long {
     pc(name)
diff --git a/src/header/unistd/sysconf.rs b/src/header/unistd/sysconf.rs
index 5e13346019..23b4fc385e 100644
--- a/src/header/unistd/sysconf.rs
+++ b/src/header/unistd/sysconf.rs
@@ -33,6 +33,7 @@ pub const _SC_SYMLOOP_MAX: c_int = 173;
 pub const _SC_HOST_NAME_MAX: c_int = 180;
 // } POSIX.1
 
+/// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/sysconf.html>.
 #[no_mangle]
 pub extern "C" fn sysconf(name: c_int) -> c_long {
     //TODO: Real values