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Improved default settings for Linux machines



I get asked about my default settings for Linux fairly frequently and was writing this in an email and decided to post it for broader use. If you have better recommendations, by all means please send me a pull request. The Edit button at the top of this page will get you there.

There are a couple groups of settings below. Most of the settings below should end up in /etc/sysctl.conf or /etc/sysctl.d/filename.conf (depending on your distro). They can be applied immediately with sudo sysctl -p /etc/sysctl.d/filename.conf.

I've applied most of these to hundreds of machines and never had an issue. That said, test in non-production first! I run the same settings across pretty much every Linux machine I touch, including laptops, Intel NUCs, Xeon workstations, and huge NUMA servers. There's more to be done for each case to get the best performance, but I think this is where almost every machine should start.

Edit: I've run across a few comments complaining about these large max values. The reason I set them high is that the machines I work on are not multi-user in any way. These settings would be insane on a shared university machine, but for a Linux workstation or server, there's only one user/application that pretty much never wants or expects to hit the ridiculously low default limits. As I mentioned, I've run these settings on likely thousands of machines over the last few years and have never seen them cause an issue; in fact quite the opposite happens: users are not surprised by silly limits like 1024 file handles or applications going away for non-deterministic amounts of time while the kernel fetches application pages from swap that were only swapped out to make room for VFS.

As of Linux >= 3.5, setting to vm.swappiness=0 disables swap entirely, but you're better off running swapoff -a since others have reported pauses.

# tell the kernel to only swap if it really needs it
vm.swappiness = 1
# increase the number of allowed mmapped files
vm.max_map_count = 1048576
# increase the number of file handles available globally
fs.file-max = 1048576
# allow up to 999999 processes with corresponding pids
# this looks nice and rarely rolls over - I've never had a problem with it.
kernel.pid_max = 999999 # unnecessary, but I like it
# seconds to delay after a kernel panic and before rebooting automatically
kernel.panic = 300

# do not enable if your machines are not physically secured
# this can be used to force reboots, kill processses, cause kernel crashes, etc without logging in
# but it's very handy when a machine is hung and you need to get control
# that said, I always enable it
kernel.sysrq = 1

These are improved defaults for opening up the Linux network stack. I recommend Googling "Linux C10k" to learn more about what they mean.

net.ipv4.ip_local_port_range = 10000 65535
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.core.netdev_max_backlog = 2500
net.core.somaxconn = 65000

These are some more advanced settings to control how much written data can be held in RAM before flushing to disk. These are generally safe to apply, but going crazy with numbers can (easily) adversely affect performance. I prefer a fairly low dirty_background setting to make sure IO doesn't get backed up. Setting these numbers really high can be useful for large file transfers that are smaller than RAM, but eventually you pay the cost of flushing to disk, so I don't recommend going crazy.

See Also:

# these will need local tuning, currently set to start flushing dirty pages at 256MB
# writes will start blocking at 2GB of dirty data, but this should only ever happen if
# your disks are far slower than your software is writing data
# If you have an older kernel, you will need to s/bytes/ratio/ and adjust accordingly.
vm.dirty_background_bytes = 268435456
vm.dirty_bytes = 1073741824

Edit: Moved the shared memory settings out of the main block since they caused problems for some desktop users. KDE, especially, seems to use a lot of shared memory. 64k is a fairly common setting, but will break KDE setups, so some people report seeing 33554432 and higher values. For now I'm going to recommend checking your distro settings and if they're already above 64k, the setting is fine and should be left alone. These are now all set to 32M, including the msgmnb which reflects the max message size. As long as apps aren't going wild with shared memory, 32M should be perfectly safe on modern hardware.

# increase the sysv ipc limits
kernel.shmmax = 33554432
kernel.msgmax = 33554432
kernel.msgmnb = 33554432

Finally, I think the whole pam limits business is useless on single-user systems (e.g. workstations, database servers), so I effectively disable it. Put this /etc/security/limits.conf or /etc/security/limits.d/disable.conf (depending on your distro & preferences). You will need to log out and back in for the limits to apply to any current logins. ssh localhost ulimit -a is a quick way to check if the settings are being applied.

* - nofile     1048576
* - memlock    unlimited
* - fsize      unlimited
* - data       unlimited
* - rss        unlimited
* - stack      unlimited
* - cpu        unlimited
* - nproc      unlimited
* - as         unlimited
* - locks      unlimited
* - sigpending unlimited
* - msgqueue   unlimited

Once these settings are applied, a lot of issues go away. Please let me know if you run into any issues either on Twitter as @AlTobey or via email at tobert@gmail.com.