Working with the Unix OS

Unix Administration
rm -rf /tmp/ *, a typo could involve several hours
Optimizing Performance
! Rebuilding the filesystem
Over time, files on the system become fragmented and spread their data over distant parts of the filesystem. To
optimize system performance, the system should ideally be copied onto tape and rebuilt from scratch to enhance
performance. The drives should also be reformatted to enhance reliability. (Only if you know what you're doing!!)
! Super User
- login as "root"
- "su" - preferred
! AT&T System V
sar - system activity reporter (-a all)
crash
! BSD
iostat
uptime
vrnstat
pstat
- number of chars (kbytes) read, written to term, disk, and cpu time as user mode, niced,
in-system mode, idle mode.
- display time, system up time, number of users, number of jobs
- virtual memory statistics - procs, memory, page, faults, cpu
- process statistics
! Tunable Parameters
NBUF - number of system buffers 250 (3 x number of ttys)
NHBUF - number of hash buffers 64
NPROC - number of process table entries/slots 250
MAXUP - number of process a user can have 20
MAXPROC - maximum number of system processes
NCLIST - character minibuffers are called clists.
TEXT
NSWAP
FILES
MOUNTS
CALLS
- number of slots in text table
- swap device should be at least size of memory
- each process has 3: stdin, stdout and stderr
- size of mount table
- callout table - so that UNIX can operate in as close to real time as possible for applications
Accounting
Unix provides facilities for monitoring system performance, network traffic etc. The administrator may need to tune
the system by reorganising filesystems or network links.
utmp & wtmp - used by accounting
struct utmp {
char ut_user[8]; /* user login name */
char ut_id[4]; /* /etc/line id */
char ut_line[12]; /* device name (console) */
short ut-pid; /* process id */
short ut_type; /* type of entry */
struct exit_status {
short e_terrnrnination; /* process termination status */
short e_exit; /* process exit status */
}
ut_exit;
time_t ut_time
/* time entry was made*/
}
od -c /etc/utmp | more
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