diff --git a/libc/spec/posix.td b/libc/spec/posix.td
@@ -58,6 +58,13 @@ def PosixSpawnFileActionsTRestrictedPtr : RestrictedPtrType<PosixSpawnFileAction
 def PosixSpawnAttrT : NamedType<"posix_spawnattr_t">;
 def RestrictedPosixSpawnAttrTPtrType : RestrictedPtrType<PosixSpawnAttrT>;
 
+def CcT : NamedType<"cc_t">;
+def SpeedT : NamedType<"speed_t">;
+def StructTermios : NamedType<"struct termios">;
+def StructTermiosPtr : PtrType<StructTermios>;
+def ConstStructTermiosPtr : ConstType<StructTermiosPtr>;
+def TcFlagT : NamedType<"tcflag_t">;
+
 def POSIX : StandardSpec<"POSIX"> {
   PtrType CharPtr = PtrType<CharType>;
   RestrictedPtrType RestrictedCharPtr = RestrictedPtrType<CharType>;
@@ -1100,6 +1107,72 @@ def POSIX : StandardSpec<"POSIX"> {
     ]
   >;
 
+  HeaderSpec Termios = HeaderSpec<
+    "termios.h",
+    [
+      Macro<"NCCS">,
+    ],
+    [CcT, PidT, SpeedT, StructTermios, TcFlagT], // Types
+    [], // Enumerations
+    [
+      FunctionSpec<
+        "cfgetispeed",
+        RetValSpec<SpeedT>,
+        [ArgSpec<ConstStructTermiosPtr>]
+      >,
+      FunctionSpec<
+        "cfgetospeed",
+        RetValSpec<SpeedT>,
+        [ArgSpec<ConstStructTermiosPtr>]
+      >,
+      FunctionSpec<
+        "cfsetispeed",
+        RetValSpec<SpeedT>,
+        [ArgSpec<StructTermiosPtr>, ArgSpec<SpeedT>]
+      >,
+      FunctionSpec<
+        "cfsetospeed",
+        RetValSpec<SpeedT>,
+        [ArgSpec<StructTermiosPtr>, ArgSpec<SpeedT>]
+      >,
+      FunctionSpec<
+        "tcdrain",
+        RetValSpec<IntType>,
+        [ArgSpec<IntType>]
+      >,
+      FunctionSpec<
+        "tcflow",
+        RetValSpec<IntType>,
+        [ArgSpec<IntType>, ArgSpec<IntType>]
+      >,
+      FunctionSpec<
+        "tcflush",
+        RetValSpec<IntType>,
+        [ArgSpec<IntType>, ArgSpec<IntType>]
+      >,
+      FunctionSpec<
+        "tcgetattr",
+        RetValSpec<IntType>,
+        [ArgSpec<IntType>, ArgSpec<StructTermiosPtr>]
+      >,
+      FunctionSpec<
+        "tcgetsid",
+        RetValSpec<PidT>,
+        [ArgSpec<IntType>]
+      >,
+      FunctionSpec<
+        "tcsendbreak",
+        RetValSpec<IntType>,
+        [ArgSpec<IntType>, ArgSpec<IntType>]
+      >,
+      FunctionSpec<
+        "tcsetattr",
+        RetValSpec<IntType>,
+        [ArgSpec<IntType>, ArgSpec<IntType>, ArgSpec<StructTermiosPtr>]
+      >,
+    ]
+  >;
+
   let Headers = [
     CType,
     Dirent,
@@ -1117,6 +1190,7 @@ def POSIX : StandardSpec<"POSIX"> {
     SysUtsName,
     SysWait,
     Time,
+    Termios,
     UniStd,
     String
   ];

diff --git a/libc/src/CMakeLists.txt b/libc/src/CMakeLists.txt
@@ -15,6 +15,7 @@ if(${LIBC_TARGET_OS} STREQUAL "linux")
   add_subdirectory(pthread)
   add_subdirectory(sched)
   add_subdirectory(sys)
+  add_subdirectory(termios)
   add_subdirectory(unistd)
 endif()
 

diff --git a/libc/src/termios/CMakeLists.txt b/libc/src/termios/CMakeLists.txt
@@ -0,0 +1,80 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+endif()
+
+add_entrypoint_object(
+  cfgetispeed
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.cfgetispeed
+)
+
+add_entrypoint_object(
+  cfsetispeed
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.cfsetispeed
+)
+
+add_entrypoint_object(
+  cfgetospeed
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.cfgetospeed
+)
+
+add_entrypoint_object(
+  cfsetospeed
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.cfsetospeed
+)
+
+add_entrypoint_object(
+  tcgetsid
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.tcgetsid
+)
+
+add_entrypoint_object(
+  tcdrain
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.tcdrain
+)
+
+add_entrypoint_object(
+  tcflow
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.tcflow
+)
+
+add_entrypoint_object(
+  tcflush
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.tcflush
+)
+
+add_entrypoint_object(
+  tcsendbreak
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.tcsendbreak
+)
+
+add_entrypoint_object(
+  tcgetattr
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.tcgetattr
+)
+
+add_entrypoint_object(
+  tcsetattr
+  ALIAS
+    DEPENDS
+      .${LIBC_TARGET_OS}.tcsetattr
+)
diff --git a/libc/src/termios/cfgetispeed.h b/libc/src/termios/cfgetispeed.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for cfgetispeed -------------------*- 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_UNISTD_CFGETISPEED_H
+#define LLVM_LIBC_SRC_UNISTD_CFGETISPEED_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+speed_t cfgetispeed(const struct termios *t);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_CFGETISPEED_H
diff --git a/libc/src/termios/cfgetospeed.h b/libc/src/termios/cfgetospeed.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for cfgetospeed -------------------*- 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_UNISTD_CFGETOSPEED_H
+#define LLVM_LIBC_SRC_UNISTD_CFGETOSPEED_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+speed_t cfgetospeed(const struct termios *t);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_CFGETOSPEED_H
diff --git a/libc/src/termios/cfsetispeed.h b/libc/src/termios/cfsetispeed.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for cfsetispeed -------------------*- 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_UNISTD_CFSETISPEED_H
+#define LLVM_LIBC_SRC_UNISTD_CFSETISPEED_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+int cfsetispeed(struct termios *t, speed_t speed);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_CFSETISPEED_H
diff --git a/libc/src/termios/cfsetospeed.h b/libc/src/termios/cfsetospeed.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for cfsetospeed -------------------*- 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_UNISTD_CFSETOSPEED_H
+#define LLVM_LIBC_SRC_UNISTD_CFSETOSPEED_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+int cfsetospeed(struct termios *t, speed_t speed);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_CFSETOSPEED_H
diff --git a/libc/src/termios/linux/CMakeLists.txt b/libc/src/termios/linux/CMakeLists.txt
@@ -0,0 +1,144 @@
+# There is no difference between input and output speeds on Linux.
+# However, since POSIX requires separate functions for setting and getting
+# of the input and output speeds, we use different entrypoints wiht the
+# same getter/setter logic.
+add_entrypoint_object(
+  cfgetispeed
+  SRCS
+    cfgetispeed.cpp
+  HDRS
+    ../cfgetispeed.h
+  DEPENDS
+    libc.include.termios
+)
+
+add_entrypoint_object(
+  cfsetispeed
+  SRCS
+    cfsetispeed.cpp
+  HDRS
+    ../cfsetispeed.h
+  DEPENDS
+    libc.include.termios
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  cfgetospeed
+  SRCS
+    cfgetospeed.cpp
+  HDRS
+    ../cfgetospeed.h
+  DEPENDS
+    libc.include.termios
+)
+
+add_entrypoint_object(
+  cfsetospeed
+  SRCS
+    cfsetospeed.cpp
+  HDRS
+    ../cfsetospeed.h
+  DEPENDS
+    libc.include.termios
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  tcgetsid
+  SRCS
+    tcgetsid.cpp
+  HDRS
+    ../tcgetsid.h
+  DEPENDS
+    libc.include.sys_syscall
+    libc.include.termios
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  tcdrain
+  SRCS
+    tcdrain.cpp
+  HDRS
+    ../tcdrain.h
+  DEPENDS
+    libc.include.sys_syscall
+    libc.include.termios
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  tcflush
+  SRCS
+    tcflush.cpp
+  HDRS
+    ../tcflush.h
+  DEPENDS
+    libc.include.sys_syscall
+    libc.include.termios
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  tcflow
+  SRCS
+    tcflow.cpp
+  HDRS
+    ../tcflow.h
+  DEPENDS
+    libc.include.sys_syscall
+    libc.include.termios
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  tcsendbreak
+  SRCS
+    tcsendbreak.cpp
+  HDRS
+    ../tcsendbreak.h
+  DEPENDS
+    libc.include.sys_syscall
+    libc.include.termios
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_header_library(
+  kernel_termios
+  HDRS
+    kernel_termios.h
+)
+
+add_entrypoint_object(
+  tcgetattr
+  SRCS
+    tcgetattr.cpp
+  HDRS
+    ../tcgetattr.h
+  DEPENDS
+    .kernel_termios
+    libc.include.sys_syscall
+    libc.include.termios
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
+
+add_entrypoint_object(
+  tcsetattr
+  SRCS
+    tcsetattr.cpp
+  HDRS
+    ../tcsetattr.h
+  DEPENDS
+    .kernel_termios
+    libc.include.sys_syscall
+    libc.include.termios
+    libc.src.__support.OSUtil.osutil
+    libc.src.errno.errno
+)
diff --git a/libc/src/termios/linux/cfgetispeed.cpp b/libc/src/termios/linux/cfgetispeed.cpp
@@ -0,0 +1,21 @@
+//===-- Linux implementation of cfgetispeed -------------------------------===//
+//
+// 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/termios/cfgetispeed.h"
+
+#include "src/__support/common.h"
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(speed_t, cfgetispeed, (const struct termios *t)) {
+  return t->c_cflag & CBAUD;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/cfgetospeed.cpp b/libc/src/termios/linux/cfgetospeed.cpp
@@ -0,0 +1,21 @@
+//===-- Linux implementation of cfgetospeed -------------------------------===//
+//
+// 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/termios/cfgetospeed.h"
+
+#include "src/__support/common.h"
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(speed_t, cfgetospeed, (const struct termios *t)) {
+  return t->c_cflag & CBAUD;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/cfsetispeed.cpp b/libc/src/termios/linux/cfsetispeed.cpp
@@ -0,0 +1,31 @@
+//===-- Linux implementation of cfsetispeed -------------------------------===//
+//
+// 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/termios/cfsetispeed.h"
+
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, cfsetispeed, (struct termios * t, speed_t speed)) {
+  constexpr speed_t NOT_SPEED_MASK = ~speed_t(CBAUD);
+  // A speed value is valid only if it is equal to one of the B<NN+> values.
+  if (t == nullptr || ((speed & NOT_SPEED_MASK) != 0)) {
+    errno = EINVAL;
+    return -1;
+  }
+
+  t->c_cflag = (t->c_cflag & NOT_SPEED_MASK) | speed;
+  t->c_ispeed = speed;
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/cfsetospeed.cpp b/libc/src/termios/linux/cfsetospeed.cpp
@@ -0,0 +1,31 @@
+//===-- Linux implementation of cfsetospeed -------------------------------===//
+//
+// 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/termios/cfsetospeed.h"
+
+#include "src/__support/common.h"
+
+#include <errno.h>
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, cfsetospeed, (struct termios * t, speed_t speed)) {
+  constexpr speed_t NOT_SPEED_MASK = ~speed_t(CBAUD);
+  // A speed value is valid only if it is equal to one of the B<NN+> values.
+  if (t == nullptr || ((speed & NOT_SPEED_MASK) != 0)) {
+    errno = EINVAL;
+    return -1;
+  }
+
+  t->c_cflag = (t->c_cflag & NOT_SPEED_MASK) | speed;
+  t->c_ospeed = speed;
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/kernel_termios.h b/libc/src/termios/linux/kernel_termios.h
@@ -0,0 +1,41 @@
+//===-- Definition of kernel's version of struct termios --------*- 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_TERMIOS_LINUX_KERNEL_TERMIOS_H
+#define LLVM_LIBC_SRC_TERMIOS_LINUX_KERNEL_TERMIOS_H
+
+#include <stddef.h>
+#include <termios.h>
+
+namespace __llvm_libc {
+
+// The kernel's struct termios is different from the libc's struct termios. The
+// kernel's syscalls expect the size and layout of its definition of struct
+// termios. So, we define a flavor of struct termios which matches that of the
+// kernel so that we can translate between the libc version and the kernel
+// version when passing struct termios objects to syscalls.
+
+// NOTE: The definitions here are generic definitions valid for most target
+// architectures including x86_64 and aarch64. Definitions on some architectures
+// deviate from these generic definitions. Adjustments have to be made for those
+// architectures.
+
+constexpr size_t KERNEL_NCCS = 19;
+
+struct kernel_termios {
+  tcflag_t c_iflag;
+  tcflag_t c_oflag;
+  tcflag_t c_cflag;
+  tcflag_t c_lflag;
+  cc_t c_line;
+  cc_t c_cc[KERNEL_NCCS];
+};
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_TERMIOS_LINUX_KERNEL_TERMIOS_H
diff --git a/libc/src/termios/linux/tcdrain.cpp b/libc/src/termios/linux/tcdrain.cpp
@@ -0,0 +1,30 @@
+//===-- Linux implementation of tcdrain -----------------------------------===//
+//
+// 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/termios/tcdrain.h"
+
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+
+#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, tcdrain, (int fd)) {
+  long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TCSBRK, 1);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/tcflow.cpp b/libc/src/termios/linux/tcflow.cpp
@@ -0,0 +1,30 @@
+//===-- Linux implementation of tcflow -----------------------------------===//
+//
+// 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/termios/tcflow.h"
+
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+
+#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, tcflow, (int fd, int action)) {
+  long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TCXONC, action);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/tcflush.cpp b/libc/src/termios/linux/tcflush.cpp
@@ -0,0 +1,30 @@
+//===-- Linux implementation of tcflush -----------------------------------===//
+//
+// 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/termios/tcflush.h"
+
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+
+#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, tcflush, (int fd, int queue_selector)) {
+  long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TCFLSH, queue_selector);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/tcgetattr.cpp b/libc/src/termios/linux/tcgetattr.cpp
@@ -0,0 +1,46 @@
+//===-- Linux implementation of tcgetattr ---------------------------------===//
+//
+// 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/termios/tcgetattr.h"
+#include "kernel_termios.h"
+
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+
+#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, tcgetattr, (int fd, struct termios *t)) {
+  __llvm_libc::kernel_termios kt;
+  long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TCGETS, &kt);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  t->c_iflag = kt.c_iflag;
+  t->c_oflag = kt.c_oflag;
+  t->c_cflag = kt.c_cflag;
+  t->c_lflag = kt.c_lflag;
+  t->c_ispeed = kt.c_cflag & CBAUD;
+  t->c_ospeed = kt.c_cflag & CBAUD;
+
+  size_t nccs = KERNEL_NCCS <= NCCS ? KERNEL_NCCS : NCCS;
+  for (size_t i = 0; i < nccs; ++i)
+    t->c_cc[i] = kt.c_cc[i];
+  if (NCCS > nccs) {
+    for (size_t i = nccs; i < NCCS; ++i)
+      t->c_cc[i] = 0;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/tcgetsid.cpp b/libc/src/termios/linux/tcgetsid.cpp
@@ -0,0 +1,31 @@
+//===-- Linux implementation of tcgetsid ----------------------------------===//
+//
+// 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/termios/tcgetsid.h"
+
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+
+#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(pid_t, tcgetsid, (int fd)) {
+  pid_t sid;
+  long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TIOCGSID, &sid);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return sid;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/tcsendbreak.cpp b/libc/src/termios/linux/tcsendbreak.cpp
@@ -0,0 +1,33 @@
+//===-- Linux implementation of tcsendbreak -------------------------------===//
+//
+// 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/termios/tcsendbreak.h"
+
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+
+#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(pid_t, tcsendbreak, (int fd, int /* unused duration */)) {
+  // POSIX leaves the behavior for non-zero duration implementation dependent.
+  // Which means that the behavior can be the same as it is when duration is
+  // zero. So, we just pass zero to the syscall.
+  long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TCSBRK, 0);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/linux/tcsetattr.cpp b/libc/src/termios/linux/tcsetattr.cpp
@@ -0,0 +1,62 @@
+//===-- Linux implementation of tcsetattr ---------------------------------===//
+//
+// 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/termios/tcsetattr.h"
+#include "kernel_termios.h"
+
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+
+#include <asm/ioctls.h> // Safe to include without the risk of name pollution.
+#include <errno.h>
+#include <sys/syscall.h> // For syscall numbers
+#include <termios.h>
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(int, tcsetattr,
+                   (int fd, int actions, const struct termios *t)) {
+  struct kernel_termios kt;
+  long cmd;
+
+  switch (actions) {
+  case TCSANOW:
+    cmd = TCSETS;
+    break;
+  case TCSADRAIN:
+    cmd = TCSETSW;
+    break;
+  case TCSAFLUSH:
+    cmd = TCSETSF;
+    break;
+  default:
+    errno = EINVAL;
+    return -1;
+  }
+
+  kt.c_iflag = t->c_iflag;
+  kt.c_oflag = t->c_oflag;
+  kt.c_cflag = t->c_cflag;
+  kt.c_lflag = t->c_lflag;
+  size_t nccs = KERNEL_NCCS <= NCCS ? KERNEL_NCCS : NCCS;
+  for (size_t i = 0; i < nccs; ++i)
+    kt.c_cc[i] = t->c_cc[i];
+  if (nccs < KERNEL_NCCS) {
+    for (size_t i = nccs; i < KERNEL_NCCS; ++i)
+      kt.c_cc[i] = 0;
+  }
+
+  long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, cmd, &kt);
+  if (ret < 0) {
+    errno = -ret;
+    return -1;
+  }
+  return 0;
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/termios/tcdrain.h b/libc/src/termios/tcdrain.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for tcdrain -----------------------*- 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_UNISTD_TCDRAIN_H
+#define LLVM_LIBC_SRC_UNISTD_TCDRAIN_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+int tcdrain(int fd);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_TCDRAIN_H
diff --git a/libc/src/termios/tcflow.h b/libc/src/termios/tcflow.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for tcflow ------------------------*- 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_UNISTD_TCFLOW_H
+#define LLVM_LIBC_SRC_UNISTD_TCFLOW_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+int tcflow(int fd, int action);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_TCFLOW_H
diff --git a/libc/src/termios/tcflush.h b/libc/src/termios/tcflush.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for tcflush -----------------------*- 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_UNISTD_TCFLUSH_H
+#define LLVM_LIBC_SRC_UNISTD_TCFLUSH_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+int tcflush(int fd, int queue_selector);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_TCFLUSH_H
diff --git a/libc/src/termios/tcgetattr.h b/libc/src/termios/tcgetattr.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for tcgetattr ---------------------*- 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_TERMIOS_TCGETATTR_H
+#define LLVM_LIBC_SRC_TERMIOS_TCGETATTR_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+int tcgetattr(int fd, struct termios *t);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_TERMIOS_TCGETATTR_H
diff --git a/libc/src/termios/tcgetsid.h b/libc/src/termios/tcgetsid.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for tcgetsid ----------------------*- 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_TERMIOS_TCGETSID_H
+#define LLVM_LIBC_SRC_TERMIOS_TCGETSID_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+pid_t tcgetsid(int fd);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_TERMIOS_TCGETSID_H
diff --git a/libc/src/termios/tcsendbreak.h b/libc/src/termios/tcsendbreak.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for tcsendbreak -------------------*- 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_UNISTD_TCSENDBREAK_H
+#define LLVM_LIBC_SRC_UNISTD_TCSENDBREAK_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+int tcsendbreak(int fd, int duration);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_UNISTD_TCSENDBREAK_H
diff --git a/libc/src/termios/tcsetattr.h b/libc/src/termios/tcsetattr.h
@@ -0,0 +1,20 @@
+//===-- Implementation header for tcsetattr ---------------------*- 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_TERMIOS_TCSETATTR_H
+#define LLVM_LIBC_SRC_TERMIOS_TCSETATTR_H
+
+#include <termios.h>
+
+namespace __llvm_libc {
+
+int tcsetattr(int fd, int actions, const struct termios *t);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_TERMIOS_TCSETATTR_H
diff --git a/libc/test/src/CMakeLists.txt b/libc/test/src/CMakeLists.txt
@@ -40,6 +40,7 @@ if(${LIBC_TARGET_OS} STREQUAL "linux")
   add_subdirectory(fcntl)
   add_subdirectory(sched)
   add_subdirectory(sys)
+  add_subdirectory(termios)
   add_subdirectory(unistd)
 endif()
 

diff --git a/libc/test/src/termios/CMakeLists.txt b/libc/test/src/termios/CMakeLists.txt
@@ -0,0 +1,22 @@
+add_libc_testsuite(libc_termios_unittests)
+
+add_libc_unittest(
+  termios_test
+  SUITE
+    libc_termios_unittests
+  SRCS
+    termios_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.include.termios
+    libc.src.fcntl.open
+    libc.src.termios.cfgetispeed
+    libc.src.termios.cfgetospeed
+    libc.src.termios.cfsetispeed
+    libc.src.termios.cfsetospeed
+    libc.src.termios.tcgetattr
+    libc.src.termios.tcgetsid
+    libc.src.termios.tcsetattr
+    libc.src.unistd.close
+    libc.test.errno_setter_matcher
+)
diff --git a/libc/test/src/termios/termios_test.cpp b/libc/test/src/termios/termios_test.cpp
@@ -0,0 +1,61 @@
+//===-- Unittests for a bunch of functions in termios.h -------------------===//
+//
+// 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/fcntl/open.h"
+#include "src/termios/cfgetispeed.h"
+#include "src/termios/cfgetospeed.h"
+#include "src/termios/cfsetispeed.h"
+#include "src/termios/cfsetospeed.h"
+#include "src/termios/tcgetattr.h"
+#include "src/termios/tcgetsid.h"
+#include "src/termios/tcsetattr.h"
+#include "src/unistd/close.h"
+#include "test/ErrnoSetterMatcher.h"
+#include "utils/UnitTest/Test.h"
+
+#include <errno.h>
+#include <termios.h>
+
+using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
+using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
+
+// We just list a bunch of smoke tests here as it is not possible to
+// test functionality at the least because we want to run the tests
+// from ninja/make which change the terminal behavior.
+
+TEST(LlvmLibcTermiosTest, SpeedSmokeTest) {
+  struct termios t;
+  errno = 0;
+  ASSERT_THAT(__llvm_libc::cfsetispeed(&t, B50), Succeeds(0));
+  ASSERT_EQ(__llvm_libc::cfgetispeed(&t), speed_t(B50));
+  ASSERT_THAT(__llvm_libc::cfsetospeed(&t, B75), Succeeds(0));
+  ASSERT_EQ(__llvm_libc::cfgetospeed(&t), speed_t(B75));
+
+  errno = 0;
+  ASSERT_THAT(__llvm_libc::cfsetispeed(&t, ~CBAUD), Fails(EINVAL));
+  errno = 0;
+  ASSERT_THAT(__llvm_libc::cfsetospeed(&t, ~CBAUD), Fails(EINVAL));
+}
+
+TEST(LlvmLibcTermiosTest, GetAttrSmokeTest) {
+  struct termios t;
+  errno = 0;
+  int fd = __llvm_libc::open("/dev/tty", O_RDONLY);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  ASSERT_THAT(__llvm_libc::tcgetattr(fd, &t), Succeeds(0));
+  ASSERT_EQ(__llvm_libc::close(fd), 0);
+}
+
+TEST(LlvmLibcTermiosTest, TcGetSidSmokeTest) {
+  int fd = __llvm_libc::open("/dev/tty", O_RDONLY);
+  ASSERT_EQ(errno, 0);
+  ASSERT_GT(fd, 0);
+  ASSERT_GT(__llvm_libc::tcgetsid(fd), pid_t(0));
+  ASSERT_EQ(__llvm_libc::close(fd), 0);
+}