Freeing up memory (RAM) on Ubuntu 8.04 Server [duplicate]
I run an Ubuntu 8.04 on a Slicehost virtual server with some lightweight server apps - apache22, svnserve, mysql, and proftpd. The only serious service limitation is RAM - 256MB is what I'm paying for.
I noticed that if I let the system run for a few days/weeks, the amount of free RAM slowly declines, and paging file is being used soon after. For example, upon rebooting I may have 60% of RAM free, next day it may be at 55%, etc.
total used free shared buffers cached
Mem: 256 114 141 0 3 50
-/+ buffers/cache: 61 194
Swap: 511 0 511
How would I prevent the amount of available memory to decline?
Edit: Here's my ps -aux listing the top memory consumers. I left out all the system processes. I can see that apache and mysql top the memory usage.
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1369 0.0 0.3 16844 952 ? S<s 00:10 0:00 /sbin/udevd --daemon
syslog 2110 0.0 0.2 12288 748 ? Ss 00:10 0:00 /sbin/syslogd -u syslog
root 2131 0.0 0.2 8128 588 ? S 00:10 0:00 /bin/dd bs 1 if /proc/kmsg of /var/run/klogd/kmsg
klog 2133 0.0 0.4 4516 1304 ? Ss 00:10 0:00 /sbin/klogd -P /var/run/klogd/kmsg
root 2154 0.0 0.4 50904 1152 ? Ss 00:10 0:00 /usr/sbin/sshd
root 2211 0.0 0.2 3932 592 ? S 00:10 0:00 /bin/sh /usr/bin/mysqld_safe
mysql 2253 0.0 8.8 161940 23252 ? Sl 00:10 0:00 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --user=mysql --pid-file=/var/run/mys
root 2254 0.0 0.2 3836 604 ? S 00:10 0:00 logger -p daemon.err -t mysqld_safe -i -t mysqld
proftpd 2340 0.0 0.5 63000 1504 ? Ss 00:10 0:00 proftpd: (accepting connections)
root 2356 0.0 0.3 18608 964 ? Ss 00:10 0:00 /usr/sbin/cron
root 2384 0.0 0.3 83360 892 ? Ss 00:10 0:00 svnserve -d -r /etc/svn/svn-rep-01
root 2387 0.0 3.5 194628 9220 ? Ss 00:10 0:00 /usr/sbin/apache2 -k start
root 2409 0.0 0.2 3852 576 tty1 Ss+ 00:10 0:00 /sbin/getty 38400 tty1
root 2410 0.0 0.5 15252 1444 ? Sl 00:10 0:00 /usr/lib/ruby/gems/1.8/gems/passenger-2.0.2/ext/apache2/ApplicationPoolServerExecutable 0 /us
www-data 2411 0.0 3.4 195880 9100 ? S 00:10 0:00 /usr/sbin/apache2 -k start
www-data 2412 0.0 7.3 205532 19400 ? S 00:10 0:00 /usr/sbin/apache2 -k start
www-data 2413 0.0 3.3 195620 8824 ? S 00:10 0:00 /usr/sbin/apache2 -k start
www-data 2414 0.0 3.4 195880 9080 ? S 00:10 0:00 /usr/sbin/apache2 -k start
www-data 2415 0.0 3.4 195888 9056 ? S 00:10 0:00 /usr/sbin/apache2 -k start
root 2416 0.0 2.4 43448 6512 ? Sl 00:10 0:00 Passenger spawn server
www-data 2437 0.0 7.7 208116 20248 ? S 00:48 0:00 /usr/sbin/apache2 -k start
www-data 2519 0.0 3.3 195644 8820 ? S 02:12 0:00 /usr/sbin/apache2 -k start
root 3026 0.0 1.1 67960 2892 ? Ss 20:53 0:00 sshd: dv [priv]
dv 3028 0.0 0.6 67960 1700 ? S 20:53 0:00 sshd: dv@pts/0
dv 3029 0.1 0.8 19392 2304 pts/0 Ss 20:53 0:00 -bash
dv 3041 0.0 0.4 15056 1092 pts/0 R+ 20:54 0:00 ps -aux
Overall, I'd like to thank everyone for their thoughtful answers and it was really hard to choose the best because each has some useful information in it.
I'll look into moving to lighthttpd or nginx, or at least reduce apache's MaxClients parameter.
You will notice that some of that is being consumed by "cache".
This is just disk read/write being cached and you can basically assume its free because it will be dumped out as soon as something more important needs it.
It makes disk IO faster. :)
I have presently 2G of disk cache on my box, makes things fast.
"free" is a poor memory analysis tool. I find "htop" a much more practical overall system management tool, which gives both a practical representation of memory use and a practical way to explore processes.
Like this, just prettier:
1 [||||| 5.0%] Tasks: 156 total, 2 running 2 [||| 2.5%] Load average: 0.29 0.30 0.31 Mem[||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| 1182/3967MB] Uptime: 5 days, 16:25:36 Swp[|| 37/2000MB] Mem:3967M used:1182M buffers:0M cache:1952M
( if you're wondering about the low uptime.. thats a laptop )
A lot of people might provide ways to negate caching to get stuff out of swap, but its more or less pointless. All you'll end up doing is reducing performance, unless you have a program that is really memory intensive , but only runs intensively every few days so that when its not running intensively it gets swapped out, and when it does come on, you cant wait the ~.5 seconds it takes to swap it back into memory from disk.
I personally can't think of any good program that matches these conditions. shrugs
The people whom wrote the kernel know more or less what they're doing in this department, I'd trust their judgment unless you're certain you know better.
as @Paul Betts said, Switching to lighttpd might help you save a bit. Depends on what you're doing, there are always a few tradeoffs.
I'm using it on my vps. Only has 96M ram and 63M swap, and its only using 26M(no joke) and 35M respectively. And there's a database running there as well. ( Postgres , but not really used )
Ignore the first line. The important numbers are on the "-/+ buffers/cache" line. Linux will clear cache and buffers to make way for processes.
My Debian server routinely shows between 2 and 10 megabytes of free space on the first line. The second line shows that I have 50 megabytes free. (With a total of 256 ram on the system)
Your numbers look fine. DO NOT clear your buffers/cache. You have more than enough free ram.
Now if you have no memory free for cache, your system will run slow. If you start using alot of swap you're going to have problems serving webpages.
you need to change your swappiness (tells the kernel how much it should swap)
# sysctl -w vm.swappiness=0
setting it to 0 will tell the VM to keep as much data in memory as possible, but you need to go and read up on whats right for you, its hard to tell, but do some experimenting and see what you can come up with.
edit the vm.swappiness line in /etc/sysctl.conf to set it up at boot
in other words, you want to use the memory as much as possible and reduce the amount of swapping that occurs on disk