Maintaining a Clean System

Memory Management

Compile a custom kernel for your system with only the drivers you require

Remove virtual consoles your not using.

Comment these lines out of your /etc/inittab file:

# Run gettys in standard runlevels
1:1234:respawn:/sbin/getty tty1 VC linux
2:234:respawn:/sbin/getty tty2 VC linux
#3:234:respawn:/sbin/getty tty3 VC linux
#4:234:respawn:/sbin/getty tty4 VC linux
#5:234:respawn:/sbin/getty tty5 VC linux
#6:234:respawn:/sbin/getty tty6 VC linux

Send init the signal to reread the inittab file:

[root@bluenote /dev]# kill -HUP 1

Remove daemons and other programs not needed from startup scripts. These programs live in /etc/rc.d on some systems and /etc/rc.d/rc?.d (where ? represents a run level 0,1,2,3,4,5,6).

top output from my development machine:

7:52pm  up 6 min,  1 user,  load average: 0.00, 0.08, 0.05
23 processes: 22 sleeping, 1 running, 0 zombie, 0 stopped
CPU states:  3.7% user,  2.8% system,  6.5% nice, 93.5% idle
Mem:  31284K av,  8080K used, 23204K free,  7264K shrd,  3588K buf
Swap: 32124K av,     0K used, 32124K free

  PID USER     PRI  NI SIZE  RES SHRD STAT %CPU %MEM  TIME COMMAND
  214 root      19  15  960  512  332 R     6.5  1.6  0:00 top
    1 root      29  15  888  364  252 S     0.0  1.1  0:16 init [3]
  185 root      24  15 1236  752  548 S     0.0  2.4  0:00 -bash
  186 root      28  15  920  384  264 S     0.0  1.2  0:00 /sbin/getty tty2 VC 
   50 root      30  15  924  444  292 S     0.0  1.4  0:00 syslogd
   59 root      30  15  992  492  268 S     0.0  1.5  0:00 klogd
   70 root      30  15  908  436  296 S     0.0  1.3  0:00 crond
   82 bin       30  15  912  392  272 S     0.0  1.2  0:00 rpc.portmap
   91 root      30  15  916  408  260 S     0.0  1.3  0:00 inetd
  102 root      30  15  944  456  312 S     0.0  1.4  0:00 rpc.mountd
  111 root      30  15  972  464  316 S     0.0  1.4  0:00 rpc.nfsd
  127 root      30  15 1288  704  484 S     0.0  2.2  0:00 sendmail: accepting 
  139 root      30  15 1112  572  504 S     0.0  1.8  0:00 httpd
  151 root      30  15  908  372  260 S     0.0  1.1  0:00 lpd
  163 root      29  15 1152  576  360 S     0.0  1.8  0:00 smbd -D
  149 nobody    30  15 1112  548  488 S     0.0  1.7  0:00 httpd
  172 root      29  15 1004  528  352 S     0.0  1.6  0:00 nmbd -D
  187 root      28  15  920  384  264 S     0.0  1.2  0:00 /sbin/getty tty3 VC

ps -alx output from the same host:

 F    UID   PID  PPID PRI NI SIZE  RSS WCHAN      STAT TTY   TIME COMMAND
  0     0     1     0  30 15  892  368 12c89c     S     ?    0:17 init [3]      
  0     0    50     1  30 15  924  444 12c89c     S     ?    0:00 syslogd
  0     0    59     1  30 15  992  492 110be8     S     ?    0:00 klogd
  0     0    70     1  30 15  908  436 109d84     S     ?    0:00 crond
  0     1    82     1  30 15  912  392 12c89c     S     ?    0:00 rpc.portmap
  0     0    91     1  30 15  916  408 12c89c     S     ?    0:00 inetd
  0     0   102     1  30 15  944  452 12c89c     S     ?    0:00 rpc.mountd
  0     0   111     1  30 15  972  460 12c89c     S     ?    0:00 rpc.nfsd
  0     0   127     1  29 15 1288  704 110be8     S     ?    0:00 sendmail: acce
  0     0   139     1  30 15 1112  572 115b06     S     ?    0:00 httpd
  0     0   151     1  30 15  908  372 12c89c     S     ?    0:00 lpd
  0     0   163     1  30 15 1152  576 110be8     S     ?    0:00 smbd -D
  0     0   172     1  30 15 1004  528 12c89c     S     ?    0:00 nmbd -D
  0     0   185     1  30 15 1248  764 115b06     S    v01   0:00 -bash
  0     0   187     1  30 15  920  384 1866db     S    v03   0:00 /sbin/getty tt
  0     0   188     1  30 15  920  384 1866db     S    v04   0:00 /sbin/getty tt
  0     0   189     1  30 15  920  372 1866db     S    v05   0:00 /sbin/getty tt
  0     0   190     1  30 15  920  372 1866db     S    v06   0:00 /sbin/getty tt
  0     0   191     1  30 15  860  292 110be8     S     ?    0:00 bdflush (daemo
  0     0   192     1  30 15  860  296 109d84     S     ?    0:00 update (bdflus
  0     0   408     1  30 15  920  384 1866db     S    v02   0:00 /sbin/getty tt
  0    99   149   139  30 15 1112  548 110be8     S     ?    0:00 httpd
  0     0   581   185  18 15  892  332 0          R    v01   0:00 ps -alx

free output from a machine after pruning unecessary daemons:

             total       used       free     shared    buffers
Mem:          6868       3848       3020       3052       2000
-/+ buffers:             1848       5020
Swap:        22172          0      22172

Use memory conscious programs with sane settings.

Program Memory Size

rxvt 1696

rxvt -sl 4096 3292

xterm 1884

xterm -sb -sl 4096 2548

nxterm 5916

nxterm -sb -sl 4096 7196

Program	Memory Size
rxvt	1696
rxvt -sl 4096	3292
xterm	1884
xterm -sb -sl 4096	2548
nxterm	5916
nxterm -sb -sl 4096	7196

Disk Management

Prevent/Control utilities from creating files.
Stop man from creating preformatted man pages (man will create preformatted man pages in /var/catman if it exists):
```
[root@bluenote /root]# mv /var/catman /var/Catman
```
Clean up font files that xdvi leaves behind:
```
[root@bluenote /root]# rm -f /var/lib/texmf/fonts/pk/ljfour/*
```
Archive/Remove the log files created in /var/log.
Remove regular files 5 days old from /tmp and regular files 30 days old from /var/tmp (some versions of Linux have shell commands to remove all files from /tmp at boot time, but that method doesn't prevent files from accumulating in /tmp during a prolonged uptime and could cause important files to be removed after a system crash).
```
[root@bluenote /root]# find /tmp -type f -mtime +5 -exec rm -f {} \;
[root@bluenote /root]# find /var/tmp -type f -mtime +30 -exec rm -f {} \;
```

Use du to select the best candidate for cleaning house on a full disk partitions.

[root@bluenote /root]# du -sk /usr/local/* | sort -rn  
93682   /usr/local/backups
83092   /usr/local/gp
54894   /usr/local/src
36696   /usr/local/postgres95
14295   /usr/local/sounds
10262   /usr/local/develop
9316    /usr/local/web
5096    /usr/local/solaris
4776    /usr/local/pics
3174    /usr/local/lib
1598    /usr/local/bin
1029    /usr/local/man
791     /usr/local/archive
12      /usr/local/lost+found
1       /usr/local/sbin
1       /usr/local/info
1       /usr/local/games
1       /usr/local/etc
1       /usr/local/doc

strip large binaries.

[root@bluenote postgres95]# du -sk bin/
11122   bin
[root@bluenote postgres95]# strip bin/*
strip: cleardbdir: File format not recognized
strip: createdb: File format not recognized
strip: createuser: File format not recognized
strip: destroydb: File format not recognized
strip: destroyuser: File format not recognized
strip: initdb: File format not recognized
[root@bluenote postgres95]# du -sk bin/
1120    bin

Use gzip with the highest level of compression: gzip -9.

User Management

Just don't allow any.

limit and ulimit

limit is a csh builtin and ulimit is a bourne/ksh/bash shell builtin. Both limits allow hard limits to be set that cannot be overridden. These limits should be set in system profile or login files so that users cannot change them.

limit example:

83 22:31/home/code> limit
cputime         unlimited
filesize        unlimited
datasize        unlimited
stacksize       8192 kbytes
coredumpsize    1000000 kbytes
memoryuse       unlimited
descriptors     256 
maxproc         256 
84 22:31/home/code> limit coredumpsize 0
85 22:31/home/code> limit
cputime         unlimited
filesize        unlimited
datasize        unlimited
stacksize       8192 kbytes
coredumpsize    0 kbytes
memoryuse       unlimited
descriptors     256 
maxproc         256

ulimit example:

22:28:34[postgres]~> ulimit -a
core file size (blocks)  1000000
data seg size (kbytes)   unlimited
file size (blocks)       unlimited
max memory size (kbytes) unlimited
stack size (kbytes)      8192
cpu time (seconds)       unlimited
max user processes       256
pipe size (512 bytes)    8
open files               256
virtual memory (kbytes)  2105343
22:35:06[postgres]~> ulimit -c 0
22:35:14[postgres]~> ulimit -a
core file size (blocks)  0
data seg size (kbytes)   unlimited
file size (blocks)       unlimited
max memory size (kbytes) unlimited
stack size (kbytes)      8192
cpu time (seconds)       unlimited
max user processes       256
pipe size (512 bytes)    8
open files               256
virtual memory (kbytes)  2105343

Last Modified: 17 April 1996

St. Louis Unix Users Group - Linux SIG