diff --git a/src/local.c b/src/local.c
index 61036b6e..239caffb 100644
--- a/src/local.c
+++ b/src/local.c
@@ -222,7 +222,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
     }
 
     ssize_t r;
-
+    errno = 0;
     r = recv(server->fd, buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -312,6 +312,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
                         s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
                     }
 #else
+                    errno = 0;
                     int s = sendto(remote->fd, remote->buf->array, remote->buf->len, MSG_FASTOPEN,
                                    (struct sockaddr *)&(remote->addr), remote->addr_len);
 #endif
@@ -349,6 +350,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
 #endif
                 }
             } else {
+                errno = 0;
                 int s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
                 if (s == -1) {
                     if (errno == EAGAIN || errno == EWOULDBLOCK) {
@@ -581,6 +583,7 @@ static void server_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(server->fd, server->buf->array + server->buf->idx,
                          server->buf->len, 0);
         if (s < 0) {
@@ -644,7 +647,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
 #ifdef ANDROID
     stat_update_cb(loop);
 #endif
-
+    errno = 0;
     ssize_t r = recv(remote->fd, server->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -679,7 +682,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
             return;
         }
     }
-
+    errno = 0;
     int s = send(server->fd, server->buf->array, server->buf->len, 0);
 
     if (s == -1) {
@@ -742,6 +745,7 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(remote->fd, remote->buf->array + remote->buf->idx,
                          remote->buf->len, 0);
         if (s < 0) {
diff --git a/src/manager.c b/src/manager.c
index 650effa8..8bd72e12 100644
--- a/src/manager.c
+++ b/src/manager.c
@@ -758,6 +758,7 @@ int main(int argc, char **argv)
     const char *homedir = pw->pw_dir;
     snprintf(working_dir, PATH_MAX, "%s/.shadowsocks", homedir);
 
+    errno = 0;
     int err = mkdir(working_dir, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
     if (err != 0 && errno != EEXIST) {
         ERROR("mkdir");
@@ -788,6 +789,7 @@ int main(int argc, char **argv)
 
         setnonblocking(sfd);
 
+        errno = 0;
         if (remove(manager_address) == -1 && errno != ENOENT) {
             ERROR("bind");
             exit(EXIT_FAILURE);
diff --git a/src/redir.c b/src/redir.c
index 93bab5ec..9a6d81e5 100644
--- a/src/redir.c
+++ b/src/redir.c
@@ -171,6 +171,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
     server_t *server              = server_recv_ctx->server;
     remote_t *remote              = server->remote;
 
+    errno = 0;
     ssize_t r = recv(server->fd, remote->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -212,6 +213,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     int s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
 
     if (s == -1) {
@@ -248,6 +250,7 @@ static void server_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(server->fd, server->buf->array + server->buf->idx,
                          server->buf->len, 0);
         if (s < 0) {
@@ -291,6 +294,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
     remote_t *remote              = remote_recv_ctx->remote;
     server_t *server              = remote->server;
 
+    errno = 0;
     ssize_t r = recv(remote->fd, server->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -320,6 +324,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
         close_and_free_server(EV_A_ server);
         return;
     }
+    errno = 0;
     int s = send(server->fd, server->buf->array, server->buf->len, 0);
 
     if (s == -1) {
@@ -424,6 +429,7 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(remote->fd, remote->buf->array + remote->buf->idx,
                          remote->buf->len, 0);
         if (s < 0) {
diff --git a/src/server.c b/src/server.c
index f26a8696..15aead4b 100644
--- a/src/server.c
+++ b/src/server.c
@@ -273,6 +273,7 @@ int setfastopen(int fd)
 #else
         int opt = 5;
 #endif
+        errno = 0;
         s = setsockopt(fd, IPPROTO_TCP, TCP_FASTOPEN, &opt, sizeof(opt));
         if (s == -1) {
             if (errno == EPROTONOSUPPORT || errno == ENOPROTOOPT) {
@@ -452,6 +453,7 @@ static remote_t *connect_to_remote(struct addrinfo *res,
             s = len;
         }
 #else
+        errno = 0;
         ssize_t s = sendto(sockfd, server->buf->array + server->buf->idx,
                            server->buf->len, MSG_FASTOPEN, res->ai_addr,
                            res->ai_addrlen);
@@ -501,6 +503,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
         len    = 0;
     }
 
+    errno = 0;
     ssize_t r = recv(server->fd, buf->array + len, BUF_SIZE - len, 0);
 
     if (r == 0) {
@@ -563,6 +566,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
             close_and_free_remote(EV_A_ remote);
             return;
         }
+        errno = 0;
         int s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
         if (s == -1) {
             if (errno == EAGAIN || errno == EWOULDBLOCK) {
@@ -833,6 +837,7 @@ static void server_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(server->fd, server->buf->array + server->buf->idx,
                          server->buf->len, 0);
         if (s < 0) {
@@ -948,6 +953,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
 
     ev_timer_again(EV_A_ & server->recv_ctx->watcher);
 
+    errno = 0;
     ssize_t r = recv(remote->fd, server->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -983,6 +989,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     int s = send(server->fd, server->buf->array, server->buf->len, 0);
 
     if (s == -1) {
@@ -1055,6 +1062,7 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(remote->fd, remote->buf->array + remote->buf->idx,
                          remote->buf->len, 0);
         if (s == -1) {
diff --git a/src/tunnel.c b/src/tunnel.c
index f581e096..892390f3 100644
--- a/src/tunnel.c
+++ b/src/tunnel.c
@@ -186,6 +186,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     ssize_t r = recv(server->fd, remote->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -221,6 +222,7 @@ static void server_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     int s = send(remote->fd, remote->buf->array, remote->buf->len, 0);
 
     if (s == -1) {
@@ -257,6 +259,7 @@ static void server_send_cb(EV_P_ ev_io *w, int revents)
         return;
     } else {
         // has data to send
+        errno = 0;
         ssize_t s = send(server->fd, server->buf->array + server->buf->idx,
                          server->buf->len, 0);
         if (s < 0) {
@@ -310,6 +313,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
     remote_t *remote              = remote_recv_ctx->remote;
     server_t *server              = remote->server;
 
+    errno = 0;
     ssize_t r = recv(remote->fd, server->buf->array, BUF_SIZE, 0);
 
     if (r == 0) {
@@ -341,6 +345,7 @@ static void remote_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    errno = 0;
     int s = send(server->fd, server->buf->array, server->buf->len, 0);
 
     if (s == -1) {
@@ -471,6 +476,7 @@ static void remote_send_cb(EV_P_ ev_io *w, int revents)
             return;
         } else {
             // has data to send
+            errno = 0;
             ssize_t s = send(remote->fd, remote->buf->array + remote->buf->idx,
                              remote->buf->len, 0);
             if (s < 0) {
diff --git a/src/utils.c b/src/utils.c
index cff3c6c7..2c07bcda 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -102,16 +102,19 @@ int run_as(const char *user)
             /* Note that we use getpwnam_r() instead of getpwnam(),
              * which returns its result in a statically allocated buffer and
              * cannot be considered thread safe. */
+            errno = 0;
             err = getpwnam_r(user, &pwdbuf, buf, buflen, &pwd);
 
             if (err == 0 && pwd) {
                 /* setgid first, because we may not be allowed to do it anymore after setuid */
+                errno = 0;
                 if (setgid(pwd->pw_gid) != 0) {
                     LOGE(
                         "Could not change group id to that of run_as user '%s': %s",
                         user, strerror(errno));
                     return 0;
                 }
+                errno = 0;
 
                 if (setuid(pwd->pw_uid) != 0) {
                     LOGE(
@@ -147,11 +150,13 @@ int run_as(const char *user)
             return 0;
         }
         /* setgid first, because we may not allowed to do it anymore after setuid */
+        errno = 0;
         if (setgid(pwd->pw_gid) != 0) {
             LOGE("Could not change group id to that of run_as user '%s': %s",
                  user, strerror(errno));
             return 0;
         }
+        errno = 0;
         if (setuid(pwd->pw_uid) != 0) {
             LOGE("Could not change user id to that of run_as user '%s': %s",
                  user, strerror(errno));
@@ -351,6 +356,7 @@ int set_nofile(int nofile)
     if (nofile <= 0) {
         FATAL("nofile must be greater than 0\n");
     }
+    errno = 0;
 
     if (setrlimit(RLIMIT_NOFILE, &limit) < 0) {
         if (errno == EPERM) {