[GH-ISSUE #3527] Documentation of frps.ini TCPKeepAlive/tcp_keepalive incorrect #2815

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opened 2026-05-05 13:49:15 -06:00 by gitea-mirror · 4 comments

gitea-mirror commented

2026-05-05 13:49:15 -06:00

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Originally created by @delaneyb on GitHub (Jul 12, 2023).
Original GitHub issue: https://github.com/fatedier/frp/issues/3527

Bug Description

Based on tracing the use of TCPKeepAlive through to handleConn in github.com/fatedier/golib/net/mux, it appears that the comparison actually performed to decide whether to call tcpConn.SetKeepAlivePeriod is if mux.keepAlive != 0, which contradicts the frps_full example, and the explanation in comments in server.go, which say that using a negative value for this setting in your config will disable tcp_keepalive probes.

According to pkg.go.dev, to explicitly disable keepalives on a Go TCPConn, we need to use SetKeepAlive(false)

frpc Version

0.48.0

frps Version

0.48.0

System Architecture

arm client/amd64 server

Configurations

frps.ini:

tcp_mux_keepalive_interval = 120
tcp_keepalive = -1

frpc.ini:
tcp_mux_keepalive_interval = 7200
dial_server_keepalive = 300

Logs

No response

Steps to reproduce

No response

Affected area

Docs
Installation
Performance and Scalability
Security
User Experience
Test and Release
Developer Infrastructure
Client Plugin
Server Plugin
Extensions
Others

Originally created by @delaneyb on GitHub (Jul 12, 2023). Original GitHub issue: https://github.com/fatedier/frp/issues/3527 ### Bug Description Based on tracing the use of `TCPKeepAlive` through to [`handleConn` in github.com/fatedier/golib/net/mux](https://github.com/fatedier/golib/blob/a1a0c648236af20e78b03094ad4f0716ae4788d7/net/mux/mux.go#L171), it appears that the comparison actually performed to decide whether to call `tcpConn.SetKeepAlivePeriod` is `if mux.keepAlive != 0`, which contradicts the [frps_full example](https://github.com/fatedier/frp/blob/8f105adbcac3b76a97a8e4744cfa31e85d4c51f1/conf/frps_full.ini#L141-L143), and the [explanation in comments in server.go](https://github.com/fatedier/frp/blob/8f105adbcac3b76a97a8e4744cfa31e85d4c51f1/pkg/config/server.go#L141-L143), which say that using a negative value for this setting in your config will disable tcp_keepalive probes. According to [pkg.go.dev](https://pkg.go.dev/net#TCPConn.SetKeepAlive), to explicitly disable keepalives on a Go TCPConn, we need to use `SetKeepAlive(false)` ### frpc Version 0.48.0 ### frps Version 0.48.0 ### System Architecture arm client/amd64 server ### Configurations frps.ini: tcp_mux_keepalive_interval = 120 tcp_keepalive = -1 frpc.ini: tcp_mux_keepalive_interval = 7200 dial_server_keepalive = 300 ### Logs _No response_ ### Steps to reproduce _No response_ ### Affected area - [X] Docs - [ ] Installation - [X] Performance and Scalability - [ ] Security - [X] User Experience - [ ] Test and Release - [ ] Developer Infrastructure - [ ] Client Plugin - [ ] Server Plugin - [ ] Extensions - [ ] Others

gitea-mirror

2026-05-05 13:49:15 -06:00

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gitea-mirror commented

2026-05-05 13:49:18 -06:00

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@fatedier commented on GitHub (Jul 12, 2023):

Have you tried set it to -1? I don't remember very clearly, but I should have tested this usage.

@fatedier commented on GitHub (Jul 12, 2023): Have you tried set it to -1? I don't remember very clearly, but I should have tested this usage.

gitea-mirror commented

2026-05-05 13:49:18 -06:00

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@delaneyb commented on GitHub (Jul 16, 2023):

Apologies for confusion, I have just tested with it set to -1 and 0 against netstat --timers. With a value of -1, it does in fact disable keepalives altogether. With a value of 0, it uses the go TCPConn default of 15 seconds

I must be misunderstanding what is getting called, or the syscall that I think is getting called when passed a negative duration just turns off keepalives for the socket

@delaneyb commented on GitHub (Jul 16, 2023): Apologies for confusion, I have just tested with it set to -1 and 0 against `netstat --timers`. With a value of -1, it does in fact disable keepalives altogether. With a value of 0, it uses the [go TCPConn default of 15 seconds](https://cs.opensource.google/go/go/+/master:src/net/tcpsock.go;l=241?q=defaultTCPKeepAlive&sq=&ss=go%2Fgo) I must be misunderstanding what is getting called, or the [syscall that I think is getting called](https://cs.opensource.google/go/go/+/refs/heads/master:src/net/tcpsockopt_unix.go;l=18;drc=fe5af1532ab9c749d880c05e0ffe0e17bf874d7f) when passed a negative duration just turns off keepalives for the socket

gitea-mirror commented

2026-05-05 13:49:19 -06:00

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@delaneyb commented on GitHub (Jul 16, 2023):

Apologies for confusion, I have just tested with it set to -1 and 0 against netstat --timers. With a value of -1, it does in fact disable keepalives altogether. With a value of 0, it uses the go TCPConn default of 15 seconds

I must be misunderstanding what is getting called, or the syscall that I think is getting called when passed a negative duration just turns off keepalives for the socket

I was testing the above with frpc for the setting dial_server_keepalive running on Linux yb-4 6.1.21-v8+ #1642 SMP PREEMPT Mon Apr 3 17:24:16 BST 2023 aarch64 GNU/Linux

However, for frps on Linux frps 5.13.0-1023-gcp #28~20.04.1-Ubuntu SMP Wed Mar 30 03:51:07 UTC 2022 x86_64 Linux, whether tcp_keepalive is set to 0 or 1, it uses the Go default of 15s

Captures on both server and client:

frpc.ini

[common]
server_addr = xxxx
server_port = 7001

; Refer to Readme.md alongside frps.ini for info on these settings
heartbeat_interval = -1
tcp_mux_keepalive_interval = 50
; Negative => probes are disabled, 0 => default 15 seconds (https://github.com/fatedier/frp/issues/3527)
dial_server_keepalive = -1
tls_enable = false

log_level = debug

[ssh-xxxx]
type = tcp
local_ip = 127.0.0.1
local_port = 22
remote_port = 0

@delaneyb commented on GitHub (Jul 16, 2023): > Apologies for confusion, I have just tested with it set to -1 and 0 against `netstat --timers`. With a value of -1, it does in fact disable keepalives altogether. With a value of 0, it uses the [go TCPConn default of 15 seconds](https://cs.opensource.google/go/go/+/master:src/net/tcpsock.go;l=241?q=defaultTCPKeepAlive&sq=&ss=go%2Fgo) > > I must be misunderstanding what is getting called, or the [syscall that I think is getting called](https://cs.opensource.google/go/go/+/refs/heads/master:src/net/tcpsockopt_unix.go;l=18;drc=fe5af1532ab9c749d880c05e0ffe0e17bf874d7f) when passed a negative duration just turns off keepalives for the socket I was testing the above with frpc for the setting `dial_server_keepalive` running on `Linux yb-4 6.1.21-v8+ #1642 SMP PREEMPT Mon Apr 3 17:24:16 BST 2023 aarch64 GNU/Linux` However, for frps on `Linux frps 5.13.0-1023-gcp #28~20.04.1-Ubuntu SMP Wed Mar 30 03:51:07 UTC 2022 x86_64 Linux`, whether `tcp_keepalive` is set to 0 or 1, it uses the [Go default of 15s](https://cs.opensource.google/go/go/+/master:src/net/tcpsock.go;l=241?q=defaultTCPKeepAlive&ss=go%2Fgo) Captures on both server and client: ![image](https://github.com/fatedier/frp/assets/18545667/30e26ff4-e58c-4f11-bed9-431c413c3dc9) frpc.ini ```ini [common] server_addr = xxxx server_port = 7001 ; Refer to Readme.md alongside frps.ini for info on these settings heartbeat_interval = -1 tcp_mux_keepalive_interval = 50 ; Negative => probes are disabled, 0 => default 15 seconds (https://github.com/fatedier/frp/issues/3527) dial_server_keepalive = -1 tls_enable = false log_level = debug [ssh-xxxx] type = tcp local_ip = 127.0.0.1 local_port = 22 remote_port = 0 ```

gitea-mirror commented

2026-05-05 13:49:21 -06:00

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@fatedier commented on GitHub (Jul 17, 2023):

I found that the behavior of this action varies on different operating systems. It would be better to explicitly specify SetKeepAlive(false).

@fatedier commented on GitHub (Jul 17, 2023): I found that the behavior of this action varies on different operating systems. It would be better to explicitly specify `SetKeepAlive(false)`.