diff --git a/libc/src/sched/linux/sched_get_priority_max.cpp b/libc/src/sched/linux/sched_get_priority_max.cpp
@@ -0,0 +1,28 @@
+//===-- Implementation of sched_get_priority_max --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_get_priority_max.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, sched_get_priority_max, (int policy)) {
+  long ret = __llvm_libc::syscall_impl(SYS_sched_get_priority_min, policy);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return ret;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/sched/linux/sched_get_priority_min.cpp b/libc/src/sched/linux/sched_get_priority_min.cpp
@@ -0,0 +1,28 @@
+//===-- Implementation of sched_get_priority_min --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_get_priority_min.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, sched_get_priority_min, (int policy)) {
+  long ret = __llvm_libc::syscall_impl(SYS_sched_get_priority_min, policy);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return ret;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/sched/linux/sched_getparam.cpp b/libc/src/sched/linux/sched_getparam.cpp
@@ -0,0 +1,29 @@
+//===-- Implementation of sched_getparam ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_getparam.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, sched_getparam,
+                   (pid_t tid, struct sched_param *param)) {
+  long ret = __llvm_libc::syscall_impl(SYS_sched_getparam, tid, param);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/sched/linux/sched_getscheduler.cpp b/libc/src/sched/linux/sched_getscheduler.cpp
@@ -0,0 +1,28 @@
+//===-- Implementation of sched_getscheduler ------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_getscheduler.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, sched_getscheduler, (pid_t tid)) {
+  long ret = __llvm_libc::syscall_impl(SYS_sched_getscheduler, tid);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/sched/linux/sched_rr_get_interval.cpp b/libc/src/sched/linux/sched_rr_get_interval.cpp
@@ -0,0 +1,29 @@
+//===-- Implementation of sched_rr_get_interval ---------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_rr_get_interval.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, sched_rr_get_interval,
+                   (pid_t tid, struct timespec *tp)) {
+  long ret = __llvm_libc::syscall_impl(SYS_sched_rr_get_interval, tid, tp);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/sched/linux/sched_setparam.cpp b/libc/src/sched/linux/sched_setparam.cpp
@@ -0,0 +1,29 @@
+//===-- Implementation of sched_setparam ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_setparam.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, sched_setparam,
+                   (pid_t tid, const struct sched_param *param)) {
+  long ret = __llvm_libc::syscall_impl(SYS_sched_setparam, tid, param);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/sched/linux/sched_setscheduler.cpp b/libc/src/sched/linux/sched_setscheduler.cpp
@@ -0,0 +1,30 @@
+//===-- Implementation of sched_setscheduler ------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/sched/sched_setscheduler.h"
+
+#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+
+#include <sys/syscall.h> // For syscall numbers.
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, sched_setscheduler,
+                   (pid_t tid, int policy, const struct sched_param *param)) {
+  long ret =
+      __llvm_libc::syscall_impl(SYS_sched_setscheduler, tid, policy, param);
+  if (ret < 0) {
+    libc_errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/sched/sched_get_priority_max.h b/libc/src/sched/sched_get_priority_max.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for sched_get_priority_max ---------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SCHED_SCHED_GET_PRIORITY_MAX_H
+#define LLVM_LIBC_SRC_SCHED_SCHED_GET_PRIORITY_MAX_H
+
+namespace __llvm_libc {
+
+int sched_get_priority_max(int policy);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SCHED_SCHED_GET_PRIORITY_MAX_H
diff --git a/libc/src/sched/sched_get_priority_min.h b/libc/src/sched/sched_get_priority_min.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for sched_get_priority_min ---------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SCHED_SCHED_GET_PRIORITY_MIN_H
+#define LLVM_LIBC_SRC_SCHED_SCHED_GET_PRIORITY_MIN_H
+
+namespace __llvm_libc {
+
+int sched_get_priority_min(int policy);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SCHED_SCHED_GET_PRIORITY_MIN_H
diff --git a/libc/src/sched/sched_getparam.h b/libc/src/sched/sched_getparam.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for sched_getparam ----------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SCHED_SCHED_GETPARAM_H
+#define LLVM_LIBC_SRC_SCHED_SCHED_GETPARAM_H
+
+#include <sched.h>
+
+namespace __llvm_libc {
+
+int sched_getparam(pid_t tid, struct sched_param *param);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SCHED_SCHED_GETPARAM_H
diff --git a/libc/src/sched/sched_getscheduler.h b/libc/src/sched/sched_getscheduler.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for sched_getscheduler -------------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SCHED_SCHED_GETSCHEDULER_H
+#define LLVM_LIBC_SRC_SCHED_SCHED_GETSCHEDULER_H
+
+#include <sched.h>
+
+namespace __llvm_libc {
+
+int sched_getscheduler(pid_t tid);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SCHED_SCHED_GETSCHEDULER_H
diff --git a/libc/src/sched/sched_rr_get_interval.h b/libc/src/sched/sched_rr_get_interval.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for sched_rr_get_interval ----------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SCHED_SCHED_RR_GET_INTERVAL_H
+#define LLVM_LIBC_SRC_SCHED_SCHED_RR_GET_INTERVAL_H
+
+#include <sched.h>
+
+namespace __llvm_libc {
+
+int sched_rr_get_interval(pid_t tid, struct timespec *tp);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SCHED_SCHED_RR_GET_INTERVAL_H
diff --git a/libc/src/sched/sched_setparam.h b/libc/src/sched/sched_setparam.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for sched_setparam ----------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SCHED_SCHED_SETPARAM_H
+#define LLVM_LIBC_SRC_SCHED_SCHED_SETPARAM_H
+
+#include <sched.h>
+
+namespace __llvm_libc {
+
+int sched_setparam(pid_t tid, const struct sched_param *param);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SCHED_SCHED_SETPARAM_H
diff --git a/libc/src/sched/sched_setscheduler.h b/libc/src/sched/sched_setscheduler.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for sched_setscheduler -------------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SCHED_SCHED_SETSCHEDULER_H
+#define LLVM_LIBC_SRC_SCHED_SCHED_SETSCHEDULER_H
+
+#include <sched.h>
+
+namespace __llvm_libc {
+
+int sched_setscheduler(pid_t tid, int policy, const struct sched_param *param);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SCHED_SCHED_SETSCHEDULER_H
diff --git a/libc/test/integration/src/pthread/CMakeLists.txt b/libc/test/integration/src/pthread/CMakeLists.txt
@@ -116,3 +116,17 @@ add_integration_test(
     libc.src.pthread.pthread_join
     libc.src.__support.CPP.atomic
 )
+
+add_integration_test(
+  pthread_join_test
+  SUITE
+    libc-pthread-integration-tests
+  SRCS
+    pthread_join_test.cpp
+  DEPENDS
+    libc.include.pthread
+    libc.include.errno
+    libc.include.stdio
+    libc.src.pthread.pthread_create
+    libc.src.pthread.pthread_join
+)
diff --git a/libc/test/integration/src/pthread/pthread_join_test.cpp b/libc/test/integration/src/pthread/pthread_join_test.cpp
@@ -0,0 +1,30 @@
+//===-- Tests for pthread_join-- ------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/pthread/pthread_create.h"
+#include "src/pthread/pthread_join.h"
+
+#include "src/errno/libc_errno.h"
+
+#include "test/IntegrationTest/test.h"
+#include <pthread.h>
+
+static void *simpleFunc(void *) { return nullptr; }
+static void nullJoinTest() {
+  pthread_t Tid;
+  ASSERT_EQ(__llvm_libc::pthread_create(&Tid, nullptr, simpleFunc, nullptr), 0);
+  ASSERT_EQ(libc_errno, 0);
+  ASSERT_EQ(__llvm_libc::pthread_join(Tid, nullptr), 0);
+  ASSERT_EQ(libc_errno, 0);
+}
+
+TEST_MAIN() {
+  libc_errno = 0;
+  nullJoinTest();
+  return 0;
+}
diff --git a/libc/test/src/sched/CMakeLists.txt b/libc/test/src/sched/CMakeLists.txt
@@ -27,6 +27,53 @@ add_libc_unittest(
     libc.src.sched.sched_yield
 )
 
+add_libc_unittest(
+  get_priority_test
+  SUITE
+    libc_sched_unittests
+  SRCS
+    get_priority_test.cpp
+  DEPENDS
+    libc.include.sched
+    libc.src.errno.errno
+    libc.src.sched.sched_get_priority_min
+    libc.src.sched.sched_get_priority_max
+)
+
+add_libc_unittest(
+  scheduler_test
+  SUITE
+    libc_sched_unittests
+  SRCS
+    param_and_scheduler_test.cpp
+  DEPENDS
+    libc.include.sched
+    libc.src.errno.errno
+    libc.src.sched.sched_getscheduler
+    libc.src.sched.sched_setscheduler
+    libc.src.sched.sched_getparam
+    libc.src.sched.sched_setparam
+    libc.src.sched.sched_get_priority_min
+    libc.src.sched.sched_get_priority_max
+    libc.src.unistd.getuid
+)
+
+add_libc_unittest(
+  sched_rr_get_interval_test
+  SUITE
+    libc_sched_unittests
+  SRCS
+    sched_rr_get_interval_test.cpp
+  DEPENDS
+    libc.include.sched
+    libc.src.errno.errno
+    libc.src.sched.sched_getscheduler
+    libc.src.sched.sched_setscheduler
+    libc.src.sched.sched_get_priority_min
+    libc.src.sched.sched_rr_get_interval
+    libc.src.unistd.getuid
+)
+
 add_libc_unittest(
   cpu_count_test
   SUITE

diff --git a/libc/test/src/sched/get_priority_test.cpp b/libc/test/src/sched/get_priority_test.cpp
@@ -0,0 +1,108 @@
+//===-- Unittests for sched_get_priority_{min,max} ------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/errno/libc_errno.h"
+#include "src/sched/sched_get_priority_max.h"
+#include "src/sched/sched_get_priority_min.h"
+#include "test/UnitTest/Test.h"
+
+#include <sched.h>
+
+TEST(LlvmLibcSchedGetPriorityTest, HandleBadPolicyTest) {
+
+  // Test arbitrary values for which there is no policy.
+  {
+    int policy = -1;
+    int max_priority = __llvm_libc::sched_get_priority_max(policy);
+    ASSERT_EQ(max_priority, -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    int min_priority = __llvm_libc::sched_get_priority_min(policy);
+    ASSERT_EQ(min_priority, -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+  }
+
+  {
+    int policy = 30;
+    int max_priority = __llvm_libc::sched_get_priority_max(policy);
+    ASSERT_EQ(max_priority, -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    int min_priority = __llvm_libc::sched_get_priority_min(policy);
+    ASSERT_EQ(min_priority, -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+  }
+
+  {
+    int policy = 80;
+    int max_priority = __llvm_libc::sched_get_priority_max(policy);
+    ASSERT_EQ(max_priority, -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    int min_priority = __llvm_libc::sched_get_priority_min(policy);
+    ASSERT_EQ(min_priority, -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+  }
+
+  {
+    int policy = 110;
+    int max_priority = __llvm_libc::sched_get_priority_max(policy);
+    ASSERT_EQ(max_priority, -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    int min_priority = __llvm_libc::sched_get_priority_min(policy);
+    ASSERT_EQ(min_priority, -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+  }
+}
+
+TEST(LlvmLibcSchedGetPriorityTest, SmokeTest) {
+  libc_errno = 0;
+
+  // We Test:
+  // SCHED_OTHER, SCHED_FIFO, SCHED_RR
+  // Linux specific test could also include:
+  // SCHED_BATCH, SCHED_ISO, SCHED_IDLE, SCHED_DEADLINE
+  {
+    int policy = SCHED_OTHER;
+    int max_priority = __llvm_libc::sched_get_priority_max(policy);
+    ASSERT_GE(max_priority, 0);
+    ASSERT_EQ(libc_errno, 0);
+    int min_priority = __llvm_libc::sched_get_priority_min(policy);
+    ASSERT_GE(min_priority, 0);
+    ASSERT_EQ(libc_errno, 0);
+
+    ASSERT_LE(max_priority, 99);
+    ASSERT_GE(min_priority, 0);
+    ASSERT_GE(max_priority, min_priority);
+  }
+
+  {
+    int policy = SCHED_FIFO;
+    int max_priority = __llvm_libc::sched_get_priority_max(policy);
+    ASSERT_GE(max_priority, 0);
+    ASSERT_EQ(libc_errno, 0);
+    int min_priority = __llvm_libc::sched_get_priority_min(policy);
+    ASSERT_GE(min_priority, 0);
+    ASSERT_EQ(libc_errno, 0);
+
+    ASSERT_LE(max_priority, 99);
+    ASSERT_GE(min_priority, 0);
+    ASSERT_GE(max_priority, min_priority);
+  }
+
+  {
+    int policy = SCHED_RR;
+    int max_priority = __llvm_libc::sched_get_priority_max(policy);
+    ASSERT_GE(max_priority, 0);
+    ASSERT_EQ(libc_errno, 0);
+    int min_priority = __llvm_libc::sched_get_priority_min(policy);
+    ASSERT_GE(min_priority, 0);
+    ASSERT_EQ(libc_errno, 0);
+
+    ASSERT_LE(max_priority, 99);
+    ASSERT_GE(min_priority, 0);
+    ASSERT_GE(max_priority, min_priority);
+  }
+}
diff --git a/libc/test/src/sched/param_and_scheduler_test.cpp b/libc/test/src/sched/param_and_scheduler_test.cpp
@@ -0,0 +1,353 @@
+//===-- Unittests for sched_{set,get}{scheduler,param} --------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/errno/libc_errno.h"
+#include "src/sched/sched_get_priority_max.h"
+#include "src/sched/sched_get_priority_min.h"
+#include "src/sched/sched_getparam.h"
+#include "src/sched/sched_getscheduler.h"
+#include "src/sched/sched_setparam.h"
+#include "src/sched/sched_setscheduler.h"
+#include "src/unistd/getuid.h"
+#include "test/UnitTest/Test.h"
+
+#include <sched.h>
+
+// We Test:
+// SCHED_OTHER, SCHED_FIFO, SCHED_RR
+//
+// TODO: Missing two tests.
+//       1) Missing permissions -> EPERM. Maybe doable by finding
+//          another pid that exists and changing its policy, but that
+//          seems risky. Maybe something with fork/clone would work.
+//
+//       2) Unkown pid -> ESRCH. Probably safe to choose a large range
+//          number or scanning current pids and getting one that doesn't
+//          exist, but again seems like it may risk actually changing
+//          sched policy on a running task.
+//
+//       Linux specific test could also include:
+//          SCHED_BATCH, SCHED_ISO, SCHED_IDLE, SCHED_DEADLINE
+
+TEST(LlvmLibcSchedParamAndSchedulerTest, SchedOtherTest) {
+  libc_errno = 0;
+
+  int policy = SCHED_OTHER;
+  bool can_set = true;
+
+  int init_policy = __llvm_libc::sched_getscheduler(0);
+  ASSERT_GE(init_policy, 0);
+  ASSERT_EQ(libc_errno, 0);
+
+  int max_priority = __llvm_libc::sched_get_priority_max(policy);
+  ASSERT_GE(max_priority, 0);
+  ASSERT_EQ(libc_errno, 0);
+  int min_priority = __llvm_libc::sched_get_priority_min(policy);
+  ASSERT_GE(min_priority, 0);
+  ASSERT_EQ(libc_errno, 0);
+
+  struct sched_param param = {min_priority};
+
+  // Negative pid
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(-1, policy, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  ASSERT_EQ(__llvm_libc::sched_getscheduler(-1), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  // Invalid Policy
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy | 128, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  // Out of bounds priority
+  param.sched_priority = min_priority - 1;
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  param.sched_priority = max_priority + 1;
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param), -1);
+  // A bit hard to test as depending if we are root or not we can run into
+  // different issues.
+  ASSERT_TRUE(libc_errno == EINVAL || libc_errno == EPERM);
+  libc_errno = 0;
+
+  // Some sched policies require permissions, so skip
+  param.sched_priority = min_priority;
+  // Success / missing permissions.
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param),
+            can_set ? 0 : -1);
+  ASSERT_TRUE(can_set ? (libc_errno == 0)
+                      : (libc_errno == EINVAL || libc_errno == EPERM));
+  libc_errno = 0;
+
+  ASSERT_EQ(__llvm_libc::sched_getscheduler(0), can_set ? policy : init_policy);
+  ASSERT_EQ(libc_errno, 0);
+
+  // Out of bounds priority
+  param.sched_priority = -1;
+  ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  param.sched_priority = max_priority + 1;
+  ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  for (int priority = min_priority; priority <= max_priority; ++priority) {
+    ASSERT_EQ(__llvm_libc::sched_getparam(0, &param), 0);
+    ASSERT_EQ(libc_errno, 0);
+    int init_priority = param.sched_priority;
+
+    param.sched_priority = priority;
+
+    // Negative pid
+    ASSERT_EQ(__llvm_libc::sched_setparam(-1, &param), -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    libc_errno = 0;
+
+    ASSERT_EQ(__llvm_libc::sched_getparam(-1, &param), -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    libc_errno = 0;
+
+    // Success / missing permissions
+    ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), can_set ? 0 : -1);
+    ASSERT_TRUE(can_set ? (libc_errno == 0)
+                        : (libc_errno == EINVAL || libc_errno == EPERM));
+    libc_errno = 0;
+
+    ASSERT_EQ(__llvm_libc::sched_getparam(0, &param), 0);
+    ASSERT_EQ(libc_errno, 0);
+
+    ASSERT_EQ(param.sched_priority, can_set ? priority : init_priority);
+  }
+  // Null test
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, nullptr), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+}
+
+TEST(LlvmLibcSchedParamAndSchedulerTest, SchedFIFOTest) {
+  libc_errno = 0;
+
+  int policy = SCHED_FIFO;
+  bool can_set = __llvm_libc::getuid() == 0;
+
+  int init_policy = __llvm_libc::sched_getscheduler(0);
+  ASSERT_GE(init_policy, 0);
+  ASSERT_EQ(libc_errno, 0);
+
+  int max_priority = __llvm_libc::sched_get_priority_max(policy);
+  ASSERT_GE(max_priority, 0);
+  ASSERT_EQ(libc_errno, 0);
+  int min_priority = __llvm_libc::sched_get_priority_min(policy);
+  ASSERT_GE(min_priority, 0);
+  ASSERT_EQ(libc_errno, 0);
+
+  struct sched_param param = {min_priority};
+
+  // Negative pid
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(-1, policy, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  ASSERT_EQ(__llvm_libc::sched_getscheduler(-1), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  // Invalid Policy
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy | 128, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  // Out of bounds priority
+  param.sched_priority = min_priority - 1;
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  param.sched_priority = max_priority + 1;
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param), -1);
+  // A bit hard to test as depending if we are root or not we can run into
+  // different issues.
+  ASSERT_TRUE(libc_errno == EINVAL || libc_errno == EPERM);
+  libc_errno = 0;
+
+  // Some sched policies require permissions, so skip
+  param.sched_priority = min_priority;
+  // Success / missing permissions.
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param),
+            can_set ? 0 : -1);
+  ASSERT_TRUE(can_set ? (libc_errno == 0)
+                      : (libc_errno == EINVAL || libc_errno == EPERM));
+  libc_errno = 0;
+
+  ASSERT_EQ(__llvm_libc::sched_getscheduler(0), can_set ? policy : init_policy);
+  ASSERT_EQ(libc_errno, 0);
+
+  // Out of bounds priority
+  param.sched_priority = -1;
+  ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  param.sched_priority = max_priority + 1;
+  ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  for (int priority = min_priority; priority <= max_priority; ++priority) {
+    ASSERT_EQ(__llvm_libc::sched_getparam(0, &param), 0);
+    ASSERT_EQ(libc_errno, 0);
+    int init_priority = param.sched_priority;
+
+    param.sched_priority = priority;
+
+    // Negative pid
+    ASSERT_EQ(__llvm_libc::sched_setparam(-1, &param), -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    libc_errno = 0;
+
+    ASSERT_EQ(__llvm_libc::sched_getparam(-1, &param), -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    libc_errno = 0;
+
+    // Success / missing permissions
+    ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), can_set ? 0 : -1);
+    ASSERT_TRUE(can_set ? (libc_errno == 0)
+                        : (libc_errno == EINVAL || libc_errno == EPERM));
+    libc_errno = 0;
+
+    ASSERT_EQ(__llvm_libc::sched_getparam(0, &param), 0);
+    ASSERT_EQ(libc_errno, 0);
+
+    ASSERT_EQ(param.sched_priority, can_set ? priority : init_priority);
+  }
+  // Null test
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, nullptr), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+}
+
+TEST(LlvmLibcSchedParamAndSchedulerTest, SchedRRTest) {
+  libc_errno = 0;
+
+  int policy = SCHED_RR;
+  bool can_set = __llvm_libc::getuid() == 0;
+
+  int init_policy = __llvm_libc::sched_getscheduler(0);
+  ASSERT_GE(init_policy, 0);
+  ASSERT_EQ(libc_errno, 0);
+
+  int max_priority = __llvm_libc::sched_get_priority_max(policy);
+  ASSERT_GE(max_priority, 0);
+  ASSERT_EQ(libc_errno, 0);
+  int min_priority = __llvm_libc::sched_get_priority_min(policy);
+  ASSERT_GE(min_priority, 0);
+  ASSERT_EQ(libc_errno, 0);
+
+  struct sched_param param = {min_priority};
+
+  // Negative pid
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(-1, policy, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  ASSERT_EQ(__llvm_libc::sched_getscheduler(-1), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  // Invalid Policy
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy | 128, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  // Out of bounds priority
+  param.sched_priority = min_priority - 1;
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  param.sched_priority = max_priority + 1;
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param), -1);
+  // A bit hard to test as depending if we are root or not we can run into
+  // different issues.
+  ASSERT_TRUE(libc_errno == EINVAL || libc_errno == EPERM);
+  libc_errno = 0;
+
+  // Some sched policies require permissions, so skip
+  param.sched_priority = min_priority;
+  // Success / missing permissions.
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param),
+            can_set ? 0 : -1);
+  ASSERT_TRUE(can_set ? (libc_errno == 0)
+                      : (libc_errno == EINVAL || libc_errno == EPERM));
+  libc_errno = 0;
+
+  ASSERT_EQ(__llvm_libc::sched_getscheduler(0), can_set ? policy : init_policy);
+  ASSERT_EQ(libc_errno, 0);
+
+  // Out of bounds priority
+  param.sched_priority = -1;
+  ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  param.sched_priority = max_priority + 1;
+  ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  for (int priority = min_priority; priority <= max_priority; ++priority) {
+    ASSERT_EQ(__llvm_libc::sched_getparam(0, &param), 0);
+    ASSERT_EQ(libc_errno, 0);
+    int init_priority = param.sched_priority;
+
+    param.sched_priority = priority;
+
+    // Negative pid
+    ASSERT_EQ(__llvm_libc::sched_setparam(-1, &param), -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    libc_errno = 0;
+
+    ASSERT_EQ(__llvm_libc::sched_getparam(-1, &param), -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    libc_errno = 0;
+
+    // Success / missing permissions
+    ASSERT_EQ(__llvm_libc::sched_setparam(0, &param), can_set ? 0 : -1);
+    ASSERT_TRUE(can_set ? (libc_errno == 0)
+                        : (libc_errno == EINVAL || libc_errno == EPERM));
+    libc_errno = 0;
+
+    ASSERT_EQ(__llvm_libc::sched_getparam(0, &param), 0);
+    ASSERT_EQ(libc_errno, 0);
+
+    ASSERT_EQ(param.sched_priority, can_set ? priority : init_priority);
+  }
+  // Null test
+  ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, nullptr), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+}
+
+TEST(LlvmLibcSchedParamAndSchedulerTest, NullParamTest) {
+  libc_errno = 0;
+
+  ASSERT_EQ(__llvm_libc::sched_setparam(0, nullptr), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+
+  ASSERT_EQ(__llvm_libc::sched_getparam(0, nullptr), -1);
+  ASSERT_EQ(libc_errno, EINVAL);
+  libc_errno = 0;
+}
diff --git a/libc/test/src/sched/sched_rr_get_interval_test.cpp b/libc/test/src/sched/sched_rr_get_interval_test.cpp
@@ -0,0 +1,74 @@
+//===-- Unittests for sched_rr_get_interval -------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/errno/libc_errno.h"
+#include "src/sched/sched_get_priority_min.h"
+#include "src/sched/sched_getscheduler.h"
+#include "src/sched/sched_rr_get_interval.h"
+#include "src/sched/sched_setscheduler.h"
+#include "src/unistd/getuid.h"
+#include "test/UnitTest/Test.h"
+
+#include <sched.h>
+
+TEST(LlvmLibcSchedRRGetIntervalTest, SmokeTest) {
+  libc_errno = 0;
+  auto SetSched = [&](int policy) {
+    int min_priority = __llvm_libc::sched_get_priority_min(policy);
+    ASSERT_GE(min_priority, 0);
+    ASSERT_EQ(libc_errno, 0);
+    struct sched_param param;
+    param.sched_priority = min_priority;
+    ASSERT_EQ(__llvm_libc::sched_setscheduler(0, policy, &param), 0);
+    ASSERT_EQ(libc_errno, 0);
+  };
+
+  auto TimespecToNs = [](struct timespec t) {
+    return t.tv_sec * 1000UL * 1000UL * 1000UL + t.tv_nsec;
+  };
+
+  struct timespec ts;
+
+  // We can only set SCHED_RR with CAP_SYS_ADMIN
+  if (__llvm_libc::getuid() == 0)
+    SetSched(SCHED_RR);
+
+  int cur_policy = __llvm_libc::sched_getscheduler(0);
+  ASSERT_GE(cur_policy, 0);
+  ASSERT_EQ(libc_errno, 0);
+
+  // We can actually run meaningful tests.
+  if (cur_policy == SCHED_RR) {
+    // Success
+    ASSERT_EQ(__llvm_libc::sched_rr_get_interval(0, &ts), 0);
+    ASSERT_EQ(libc_errno, 0);
+
+    // Check that numbers make sense (liberal bound of 10ns - 30sec)
+    ASSERT_GT(TimespecToNs(ts), 10UL);
+    ASSERT_LT(TimespecToNs(ts), 30UL * 1000UL * 1000UL * 1000UL);
+
+    // Null timespec
+    ASSERT_EQ(__llvm_libc::sched_rr_get_interval(0, nullptr), -1);
+    ASSERT_EQ(libc_errno, EFAULT);
+    libc_errno = 0;
+
+    // Negative pid
+    ASSERT_EQ(__llvm_libc::sched_rr_get_interval(-1, &ts), -1);
+    ASSERT_EQ(libc_errno, EINVAL);
+    libc_errno = 0;
+  }
+
+  // Negative tests don't have SCHED_RR set
+  SetSched(SCHED_OTHER);
+  ASSERT_EQ(__llvm_libc::sched_rr_get_interval(0, &ts), 0);
+  ASSERT_EQ(libc_errno, 0);
+  libc_errno = 0;
+
+  // TODO: Missing unkown pid -> ESRCH. This is read only so safe to try a few
+  //       unlikely values.
+}