Debian – How to reset sysctl to it’s OS defaults

debianresetsysctl

I couldn't find an answer in the man pages for sysctl. My sysctl.conf file is still at it's default state, I'm testing several values and loaded new settings via sysctl -p newsettings.conf. I though it would be sufficient for reseting to do sysctl -p (which means that it reads the values from sysctl.conf). But a fast sysctl -a | grep domain revealed that there are still the old settings.

Any ideas?

Best Answer

As far as I know there is no "undo" for sysctl -- You need to re-enter the default settings (typically /etc/sysctl.conf simply does not specify defaults, so re-reading it won't revert your changes unless there's an explicit setting).

If you do not know your default settings a reboot will get them back, and you can then list them with sysctl -a (store this somewhere for reference). If you have another mostly-identical machine around you can grab the sysctl -a output from that host instead of rebooting.

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FreeBSD performance tuning: Sysctl parameter, loader.conf, kernel

I'd recommend against options IPFIREWALL_DEFAULT_TO_ACCEPT. The default is to Default to Deny. The firewall comes up with just one rule deny ip from any to any and stays that way until a script configures exactly what traffic should get through.

Follow-Up Note: RSA (one of the world's leading security technology companies) was hacked recently when part of their firewall was disabled during a maintenance window. This really underscores how quickly a system can be compromised given the right conditions.

If you insist on disabling the firewall until you explicitly block unwanted traffic, please consider using the sysctl available by adding net.inet.ip.fw.default_to_accept=1 to loader.conf. This has the added benefit of being easily modified (no recompiling the kernel) if you change your mind at some point in the future.

Linux – Sysctl config for high performance, large activity

define large activity? large number of files open? large files being transferred? lots of slow clients? This is taken off a machine that runs nginx serving 900+mb/sec of 120k or smaller images on a Quad Core Xeon 2.4. The settings on a server that does streaming content are much different. Each machine config is different based on the requirements. Blindly implementing these could make your performance better or worse.

fs/file-max=60000
fs/dir-notify-enable=0

net/ipv4/tcp_keepalive_time=600
net/core/rmem_max=262143
net/core/rmem_default=262143
net/core/wmem_max=262143
net/core/wmem_default=262143
net/ipv4/tcp_sack=0
net/ipv4/tcp_timestamps=0

net/nf_conntrack_max=262143
net/ipv4/tcp_frto=0

net.ipv4.tcp_sack=1
net.ipv4.tcp_timestamps=1
net.ipv4.tcp_wmem = 4096 65536 4194304
net.ipv4.tcp_rmem = 4096 87380 4194304

net.ipv4.tcp_fin_timeout = 1
net.ipv4.tcp_tw_recycle = 1
net.core.wmem_max = 16777216
net.core.rmem_max = 16777216
net.core.wmem_default = 16777216
net.core.rmem_default = 16777216
net.core.netdev_max_backlog = 262144
net.core.somaxconn = 262144

net.ipv4.tcp_syncookies = 0
net.ipv4.tcp_max_orphans = 262144
net.ipv4.tcp_max_syn_backlog = 262144
net.ipv4.tcp_synack_retries = 2
net.ipv4.tcp_syn_retries = 2

While the information on this page is somewhat old, much of it still applies:

http://www.acc.umu.se/~maswan/linux-netperf.txt www.ibm.com/developerworks/linux/library/l-hisock.html slaptijack.com/system-administration/linux-tcp-performance-tuning/

Best Answer

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FreeBSD performance tuning: Sysctl parameter, loader.conf, kernel

Linux – Sysctl config for high performance, large activity

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