diff --git a/bench/fails/fails.go b/bench/fails/fails.go
index b35e0fbcd..76ec23f68 100644
--- a/bench/fails/fails.go
+++ b/bench/fails/fails.go
@@ -14,8 +14,6 @@ const (
 	ErrApplication failure.StringCode = "error application"
 	// ErrTimeout はタイムアウトエラー。基本は大目に見る。
 	ErrTimeout failure.StringCode = "error timeout"
-	// ErrTemporary は一時的なエラー。基本は大目に見る。
-	ErrTemporary failure.StringCode = "error temporary"
 )
 
 var (
@@ -82,9 +80,6 @@ func (e *Errors) Add(err error) {
 		case ErrTimeout:
 			msg += "（タイムアウトしました）"
 			e.trivial++
-		case ErrTemporary:
-			msg += "（一時的なエラー）"
-			e.trivial++
 		case ErrApplication:
 			e.application++
 		default:
diff --git a/bench/server/shipment.go b/bench/server/shipment.go
index b94389ecd..c8d9f0ed4 100644
--- a/bench/server/shipment.go
+++ b/bench/server/shipment.go
@@ -158,8 +158,6 @@ func (c *shipmentStore) Get(key string) (shipment, bool) {
 }
 
 func init() {
-	rand.Seed(time.Now().UnixNano())
-
 	shipmentHash = sha1.New()
 	shipmentHash.Write(SecretSeed)
 }
diff --git a/bench/session/session.go b/bench/session/session.go
index 453298d8c..d85e0503b 100644
--- a/bench/session/session.go
+++ b/bench/session/session.go
@@ -3,7 +3,6 @@ package session
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net"
 	"net/http"
 	"net/url"
@@ -150,7 +149,7 @@ func checkStatusCode(res *http.Response, expectedStatusCode int) error {
 	prefixMsg := fmt.Sprintf("%s %s", res.Request.Method, res.Request.URL.Path)
 
 	if res.StatusCode != expectedStatusCode {
-		b, err := ioutil.ReadAll(res.Body)
+		b, err := io.ReadAll(res.Body)
 		if err != nil {
 			return failure.Wrap(err, failure.Message(prefixMsg+": bodyの読み込みに失敗しました"))
 		}
@@ -166,7 +165,7 @@ func checkStatusCodeWithMsg(res *http.Response, expectedStatusCode int, msg stri
 	prefixMsg := fmt.Sprintf("%s %s", res.Request.Method, res.Request.URL.Path)
 
 	if res.StatusCode != expectedStatusCode {
-		b, err := ioutil.ReadAll(res.Body)
+		b, err := io.ReadAll(res.Body)
 		if err != nil {
 			return failure.Wrap(err, failure.Message(prefixMsg+": bodyの読み込みに失敗しました "+msg))
 		}
@@ -184,8 +183,6 @@ func (s *Session) Do(req *http.Request) (*http.Response, error) {
 		if nerr, ok := err.(net.Error); ok {
 			if nerr.Timeout() {
 				return nil, failure.Translate(err, fails.ErrTimeout)
-			} else if nerr.Temporary() {
-				return nil, failure.Translate(err, fails.ErrTemporary)
 			}
 		}
 
diff --git a/bench/session/webapp.go b/bench/session/webapp.go
index 647713c59..54e9fc25a 100644
--- a/bench/session/webapp.go
+++ b/bench/session/webapp.go
@@ -7,7 +7,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"mime/multipart"
 	"net/http"
 	"net/url"
@@ -509,7 +508,7 @@ func (s *Session) ShipDone(ctx context.Context, itemID int64) error {
 		return err
 	}
 
-	_, err = ioutil.ReadAll(res.Body)
+	_, err = io.ReadAll(res.Body)
 	if err != nil {
 		return failure.Wrap(err, failure.Messagef("POST /ship_done: bodyの読み込みに失敗しました (item_id: %d)", itemID))
 	}
@@ -540,7 +539,7 @@ func (s *Session) Complete(ctx context.Context, itemID int64) error {
 		return err
 	}
 
-	_, err = ioutil.ReadAll(res.Body)
+	_, err = io.ReadAll(res.Body)
 	if err != nil {
 		return failure.Wrap(err, failure.Messagef("POST /complete: bodyの読み込みに失敗しました (item_id: %d)", itemID))
 	}
diff --git a/cmd/bench-worker/main.go b/cmd/bench-worker/main.go
index 691e8cfc8..d3babe130 100644
--- a/cmd/bench-worker/main.go
+++ b/cmd/bench-worker/main.go
@@ -231,8 +231,9 @@ func runBenchmarker(benchmarkerPath string, job *Job) (*BenchmarkResult, error)
 		fmt.Sprintf("-shipment-url=https://%s", fmt.Sprintf("shipment%s.isucon9q.catatsuy.org", suffix)),
 		fmt.Sprintf("-target-url=https://%s", target.GlobalIP),
 		fmt.Sprintf("-allowed-ips=%s", strings.Join(allowedIPs, ",")),
-		fmt.Sprintf("-data-dir=/home/isucon/isucari/initial-data"),
-		fmt.Sprintf("-static-dir=/home/isucon/isucari/webapp/public/static"))
+		"-data-dir=/home/isucon/isucari/initial-data",
+		"-static-dir=/home/isucon/isucari/webapp/public/static",
+	)
 
 	var (
 		stdout bytes.Buffer
diff --git a/cmd/bench/main.go b/cmd/bench/main.go
index 1b2164382..756520edf 100644
--- a/cmd/bench/main.go
+++ b/cmd/bench/main.go
@@ -5,7 +5,6 @@ import (
 	"encoding/json"
 	"flag"
 	"log"
-	"math/rand"
 	"net"
 	"os"
 	"sort"
@@ -39,8 +38,6 @@ type Config struct {
 }
 
 func init() {
-	rand.Seed(time.Now().UnixNano())
-
 	log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)
 }
 
diff --git a/webapp/go/api.go b/webapp/go/api.go
index f26387fc3..d31a3e28f 100644
--- a/webapp/go/api.go
+++ b/webapp/go/api.go
@@ -4,7 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"net/http"
 )
 
@@ -68,7 +68,7 @@ func APIPaymentToken(paymentURL string, param *APIPaymentServiceTokenReq) (*APIP
 	defer res.Body.Close()
 
 	if res.StatusCode != http.StatusOK {
-		b, err := ioutil.ReadAll(res.Body)
+		b, err := io.ReadAll(res.Body)
 		if err != nil {
 			return nil, fmt.Errorf("failed to read res.Body and the status code of the response from shipment service was not 200: %v", err)
 		}
@@ -103,7 +103,7 @@ func APIShipmentCreate(shipmentURL string, param *APIShipmentCreateReq) (*APIShi
 	defer res.Body.Close()
 
 	if res.StatusCode != http.StatusOK {
-		b, err := ioutil.ReadAll(res.Body)
+		b, err := io.ReadAll(res.Body)
 		if err != nil {
 			return nil, fmt.Errorf("failed to read res.Body and the status code of the response from shipment service was not 200: %v", err)
 		}
@@ -138,14 +138,14 @@ func APIShipmentRequest(shipmentURL string, param *APIShipmentRequestReq) ([]byt
 	defer res.Body.Close()
 
 	if res.StatusCode != http.StatusOK {
-		b, err := ioutil.ReadAll(res.Body)
+		b, err := io.ReadAll(res.Body)
 		if err != nil {
 			return nil, fmt.Errorf("failed to read res.Body and the status code of the response from shipment service was not 200: %v", err)
 		}
 		return nil, fmt.Errorf("status code: %d; body: %s", res.StatusCode, b)
 	}
 
-	return ioutil.ReadAll(res.Body)
+	return io.ReadAll(res.Body)
 }
 
 func APIShipmentStatus(shipmentURL string, param *APIShipmentStatusReq) (*APIShipmentStatusRes, error) {
@@ -167,7 +167,7 @@ func APIShipmentStatus(shipmentURL string, param *APIShipmentStatusReq) (*APIShi
 	defer res.Body.Close()
 
 	if res.StatusCode != http.StatusOK {
-		b, err := ioutil.ReadAll(res.Body)
+		b, err := io.ReadAll(res.Body)
 		if err != nil {
 			return nil, fmt.Errorf("failed to read res.Body and the status code of the response from shipment service was not 200: %v", err)
 		}