Troubleshooting sysctl: cannot stat /proc/sys/net/ipv4/tcp_tw_recycle: No such file or directory
net.ipv4.tcp_tw_recycle = 0in
/etc/sysctl.confcaused error: sysctl: cannot stat /proc/sys/net/ipv4/tcp_tw_recycle: No such file or directory
Per Linux kernel document networking/ip-sysctl.txt:
tcp_tw_recycle - BOOLEAN
Enable fast recycling TIME-WAIT sockets. Default value is 0. It should not be changed without advice/request of technical experts.
This documentation is not clear what is mechanism and what is the side effect.
Symptom - sysctl: cannot stat /proc/sys/net/ipv4/tcp_tw_recycle: No such file or directory
When I tried to put following line into
net.ipv4.tcp_tw_recycle = 0
sysctl -p to reload it, I got following error:
$ sudo sysctl -p sysctl: cannot stat /proc/sys/net/ipv4/tcp_tw_recycle: No such file or directory
net.ipv4.tcp_tw_recycle has been removed
4.12 on 2017.
Check kernel version:
$ uname -a Linux pi3 4.19.97-v7+ #1294 SMP
My kernel version is
4.19 which is newer than
net.ipv4.tcp_tw_recycle is not available anymore.
This error can be safely ignored.
Should not set this option anymore.
Reason to remove
Per kernel git commit history,
tcp_tw_recycle is not functional and cause problem.
The tcp_tw_recycle was already broken for connections behind NAT, since the per-destination timestamp is not monotonically increasing for multiple machines behind a single destination address.
After the randomization of TCP timestamp offsets in commit 8a5bd45f6616 (tcp: randomize tcp timestamp offsets for each connection), the tcp_tw_recycle is broken for all types of connections for the same reason: the timestamps received from a single machine is not monotonically increasing, anymore.
Remove tcp_tw_recycle, since it is not functional. Also, remove the PAWSPassive SNMP counter since it is only used for tcp_tw_recycle, and simplify tcp_v4_route_req and tcp_v6_route_req since the strict argument is only set when tcp_tw_recycle is enabled.
Consider to use
tcp_tw_reuse by set to
1 to improve network server performance:
net.ipv4.tcp_tw_reuse = 1
tcp_tw_reuse - INTEGER
Enable reuse of TIME-WAIT sockets for new connections when it is safe from protocol viewpoint.
- 0 - disable
- 1 - global enable
- 2 - enable for loopback traffic only
It should not be changed without advice/request of technical experts.
- Linux kernel commit: tcp: remove tcp_tw_recycle
- Linux kernel Documentation/networking/ip-sysctl.txt
- Coping with the TCP TIME-WAIT state on busy Linux servers
- Linux Kernel documentation: /proc/sys/net/ipv4/* Variables
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