diff --git a/plugins/modbus/modbus.c b/plugins/modbus/modbus.c
index e3e0f427..89456ac7 100644
--- a/plugins/modbus/modbus.c
+++ b/plugins/modbus/modbus.c
@@ -182,7 +182,7 @@ int modbus_m_write_req(char *buf, uint8_t device_address,
     uint8_t * data8  = (uint8_t *) &request[1];
     uint16_t *data16 = (uint16_t *) &request[1];
     uint32_t *data32 = (uint32_t *) &request[1];
-    uint16_t *crc;
+    uint16_t *crc    = NULL;
 
     uint16_t len = sizeof(*code) + sizeof(*request) + sizeof(*crc);
 
diff --git a/plugins/modbus/modbus_point.c b/plugins/modbus/modbus_point.c
index 5f08f117..e68f2e62 100644
--- a/plugins/modbus/modbus_point.c
+++ b/plugins/modbus/modbus_point.c
@@ -414,8 +414,8 @@ static void insert_point(modbus_point_context_t *ctx, modbus_point_t *point)
 
 static void insert_cmd(modbus_point_context_t *ctx, modbus_point_t *point)
 {
-    bool              exist = false;
-    modbus_function_e function;
+    bool              exist    = false;
+    modbus_function_e function = 0;
 
     switch (point->area) {
     case MODBUS_AREA_COIL:
diff --git a/plugins/mqtt/command/read_write.c b/plugins/mqtt/command/read_write.c
index a0f7fdd6..0ba90ace 100644
--- a/plugins/mqtt/command/read_write.c
+++ b/plugins/mqtt/command/read_write.c
@@ -331,7 +331,7 @@ int command_rw_write_request(neu_plugin_t *plugin, neu_json_mqtt_t *mqtt,
     neu_datatag_table_t *table = neu_system_get_datatags_table(plugin, node_id);
 
     neu_int_val_t        int_val;
-    neu_data_val_t *     val;
+    neu_data_val_t *     val   = NULL;
     union neu_json_value value = write_req->value;
     neu_datatag_t *      tag =
         neu_datatag_tbl_get_by_name(table, write_req->tag_name);
diff --git a/plugins/mqtt/util.c b/plugins/mqtt/util.c
index 53bf71a5..604fad86 100644
--- a/plugins/mqtt/util.c
+++ b/plugins/mqtt/util.c
@@ -177,10 +177,25 @@ int mqtt_option_init(neu_config_t *config, neu_mqtt_option_t *option)
             return -1;
         }
 
-        char workdir[PATH_MAX + 1] = { 0 };
-        getcwd(workdir, sizeof(workdir));
-        sprintf(ca_file, "%s/%s/%s", workdir, MQTT_CERT_PATH, MQTT_CA_FILE);
-        sprintf(ca_path, "%s/%s", workdir, MQTT_CERT_PATH);
+        char  workdir[PATH_MAX + 1] = { 0 };
+        char *ret_dir               = getcwd(workdir, sizeof(workdir));
+        if (NULL == ret_dir) {
+            free(ca.v.val_str);
+            return -1;
+        }
+        ret = snprintf(ca_file, sizeof(ca_file), "%s/%s/%s", workdir,
+                       MQTT_CERT_PATH, MQTT_CA_FILE);
+        if (ret < 0) {
+            free(ca.v.val_str);
+            return -1;
+        }
+
+        ret = snprintf(ca_path, sizeof(ca_path), "%s/%s", workdir,
+                       MQTT_CERT_PATH);
+        if (ret < 0) {
+            free(ca.v.val_str);
+            return -1;
+        }
 
         ret = b64_file_store(ca.v.val_str, ca_file);
         free(ca.v.val_str);
@@ -192,12 +207,20 @@ int mqtt_option_init(neu_config_t *config, neu_mqtt_option_t *option)
     }
 
     if (0 == strcmp(option->connection, "ssl://")) {
-        char workdir[PATH_MAX + 1] = { 0 };
-        getcwd(workdir, sizeof(workdir));
+        char  workdir[PATH_MAX + 1] = { 0 };
+        char *ret_dir               = getcwd(workdir, sizeof(workdir));
+        if (NULL == ret_dir) {
+            return -1;
+        }
 
         if (NULL != cert.v.val_str && 0 < strlen(cert.v.val_str)) {
-            sprintf(cert_file, "%s/%s/%s", workdir, MQTT_CERT_PATH,
-                    MQTT_CERT_FILE);
+            ret = snprintf(cert_file, sizeof(cert_file), "%s/%s/%s", workdir,
+                           MQTT_CERT_PATH, MQTT_CERT_FILE);
+            if (ret < 0) {
+                free(cert.v.val_str);
+                cert.v.val_str = NULL;
+                return -1;
+            }
 
             ret = b64_file_store(cert.v.val_str, cert_file);
             free(cert.v.val_str);
@@ -209,8 +232,13 @@ int mqtt_option_init(neu_config_t *config, neu_mqtt_option_t *option)
         }
 
         if (NULL != key.v.val_str && 0 < strlen(key.v.val_str)) {
-            sprintf(key_file, "%s/%s/%s", workdir, MQTT_CERT_PATH,
-                    MQTT_KEY_FILE);
+            ret = snprintf(key_file, sizeof(key_file), "%s/%s/%s", workdir,
+                           MQTT_CERT_PATH, MQTT_KEY_FILE);
+            if (ret < 0) {
+                free(key.v.val_str);
+                key.v.val_str = NULL;
+                return -1;
+            }
 
             ret = b64_file_store(key.v.val_str, key_file);
             free(key.v.val_str);
diff --git a/plugins/restful/log_handle.c b/plugins/restful/log_handle.c
index faec6afe..4681a0b5 100644
--- a/plugins/restful/log_handle.c
+++ b/plugins/restful/log_handle.c
@@ -148,7 +148,11 @@ static inline bool validate_cache(FILE *fp, int level, uint64_t since,
 
         // check against file modification, maybe due to log rotation
         fseek(fp, g_log_cache_.offset_end, SEEK_SET);
-        fgets(buf, sizeof(buf), fp);
+        char *ret = fgets(buf, sizeof(buf), fp);
+        if (NULL == ret) {
+            return false;
+        }
+
         if (NULL != strptime(buf, LOG_TIME_FMT, &tm)) {
             ts = mktime(&tm);
             if (ts == g_log_cache_.time) {
diff --git a/plugins/sample/plugin_sample_app.c b/plugins/sample/plugin_sample_app.c
index 3b9efcf9..f940b23a 100644
--- a/plugins/sample/plugin_sample_app.c
+++ b/plugins/sample/plugin_sample_app.c
@@ -206,8 +206,8 @@ static void *sample_app_work_loop(void *arg)
     /* example of get group configs */
     neu_cmd_get_grp_configs_t  get_grps_cmd;
     neu_reqresp_grp_configs_t *resp_grps;
-    neu_taggrp_config_t *      grp_config;
-    result = NULL;
+    neu_taggrp_config_t *      grp_config = NULL;
+    result                                = NULL;
 
     get_grps_cmd.node_id = dst_node_id;
     sync_cmd.req_type    = NEU_REQRESP_GET_GRP_CONFIGS;
diff --git a/src/base/neu_tag.c b/src/base/neu_tag.c
index 2ee85c55..02fa9922 100644
--- a/src/base/neu_tag.c
+++ b/src/base/neu_tag.c
@@ -412,7 +412,7 @@ int neu_datatag_string_etoh(char *str, int len)
         t[i] = str[i * 2];
     }
     memset(str, 0, len);
-    strncpy(str, t, strlen(t));
+    strncpy(str, t, strlen(str));
 
     free(t);
     return len / 2;
@@ -426,7 +426,7 @@ int neu_datatag_string_dtoh(char *str, int len)
         t[i] = str[i * 2 + 1];
     }
     memset(str, 0, len);
-    strncpy(str, t, strlen(t));
+    strncpy(str, t, strlen(str));
 
     free(t);
     return len / 2;
diff --git a/src/base/tag_table.c b/src/base/tag_table.c
index 800a2f77..218533ac 100644
--- a/src/base/tag_table.c
+++ b/src/base/tag_table.c
@@ -113,7 +113,8 @@ int neu_tag_table_add(neu_tag_table_t *tbl, neu_tag_t *tag)
         elem = calloc(1, sizeof(struct tag_elem));
 
         elem->tag = *tag;
-        strncpy(elem->name, tag->name, strlen(tag->name));
+        strncpy(elem->name, tag->name, sizeof(elem->name));
+
         HASH_ADD_STR(tbl->tags, name, elem);
 
         update_timestamp(tbl);
diff --git a/src/daemon.c b/src/daemon.c
index b6e372b4..ed52b5cf 100644
--- a/src/daemon.c
+++ b/src/daemon.c
@@ -17,6 +17,7 @@
  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  **/
 
+#include <assert.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <sys/resource.h>
@@ -37,6 +38,7 @@ void daemonize()
     pid_t            pid;
     struct rlimit    rl;
     struct sigaction sa;
+    int              ret = -1;
 
     // clear file creation mask
     umask(0);
@@ -75,8 +77,10 @@ void daemonize()
 
     // attach file descriptors 0, 1 and 2 to /dev/null
     open("/dev/null", O_RDWR);
-    dup(0);
-    dup(0);
+    ret = dup(0);
+    assert(ret != -1);
+    ret = dup(0);
+    assert(ret != -1);
 }
 
 static inline int lock_file(int fd)
@@ -91,8 +95,10 @@ static inline int lock_file(int fd)
 
 int neuron_already_running()
 {
-    int  fd      = -1;
-    char buf[16] = { 0 };
+    int     fd      = -1;
+    char    buf[16] = { 0 };
+    int     ret     = -1;
+    ssize_t size    = -1;
 
     fd = open(NEURON_DAEMON_LOCK_FNAME, O_RDWR | O_CREAT,
               S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
@@ -111,8 +117,12 @@ int neuron_already_running()
     }
 
     // write process id to file
-    ftruncate(fd, 0);
+    ret = ftruncate(fd, 0);
+    assert(ret != -1);
+
     snprintf(buf, sizeof(buf), "%ld", (long) getpid());
-    write(fd, buf, strlen(buf) + 1);
+    size = write(fd, buf, strlen(buf) + 1);
+    assert(size != -1);
+
     return 0;
 }
diff --git a/src/event/event_linux.c b/src/event/event_linux.c
index 9c034be8..84c49f79 100644
--- a/src/event/event_linux.c
+++ b/src/event/event_linux.c
@@ -16,6 +16,7 @@
  * along with this program; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  **/
+#include <assert.h>
 #include <errno.h>
 #include <pthread.h>
 #include <stdbool.h>
@@ -95,7 +96,8 @@ static void *event_loop(void *arg)
             if ((event.events & EPOLLIN) == EPOLLIN) {
                 uint64_t t;
 
-                read(data->fd, &t, sizeof(t));
+                ssize_t size = read(data->fd, &t, sizeof(t));
+                assert(size != -1);
 
                 ret = data->callback.timer(data->usr_data);
             }
diff --git a/src/parser/neu_json_fn.c b/src/parser/neu_json_fn.c
index a07f0c9c..ff5154b6 100644
--- a/src/parser/neu_json_fn.c
+++ b/src/parser/neu_json_fn.c
@@ -188,7 +188,7 @@ neu_data_val_t *neu_parse_write_req_to_val(neu_json_write_req_t *req,
     neu_fixed_array_t *array = neu_fixed_array_new(1, sizeof(neu_int_val_t));
 
     neu_int_val_t   iv;
-    neu_data_val_t *v;
+    neu_data_val_t *v = NULL;
 
     switch (tag->type) {
     case NEU_DTYPE_UINT8:
diff --git a/src/utils/neu_jwt.c b/src/utils/neu_jwt.c
index 2f7604e6..9b7c61f7 100644
--- a/src/utils/neu_jwt.c
+++ b/src/utils/neu_jwt.c
@@ -107,7 +107,7 @@ int neu_jwt_new(char **token)
     }
 
     *token = str_jwt;
-    strncpy(token_local, *token, strlen(*token));
+    strncpy(token_local, *token, sizeof(token_local) - 1);
 
     jwt_free(jwt);