1. CHAPTER 8 ( , )
John Carelli, Instructor Kutztown University

2. Definition - execution of a command
PID - Process IDentification number
Hierarchical structure
processes can spawn children (sub-processes)
pstree command

3. https://goo.gl/images/381BdN

4. Definition - the lifetime of a user login process
job - a command pipeline
(which may be a simple command)
 ; - command separator
 & - run in the background

5. history - log of past commands
jobs - currently running jobs
kill, (stop, in tcsh) - terminate a process
fg, bg - move process to for/background
ps - list processes
top - view top running processes
uptime - time system has been running
free - report on available memory
pstree - show process tree
nohup - run command immune to hangups

6. ps command Used to view processes
Unix, BSD, and GNU (long format) options
Unix: single dash
BSD: no dash
GNU double dash
Current user’s processes
ps ux
ps –ly (or ps –F …)
All user’s processes
ps aux
ps –ely
Note: these output different information!

7. strace - trace system calls on a command
truss (not implemented) is similar
gprof (prof) - compile c/c++ programs with –gp option
- run gprof on executable to get profile
- see profile.c example

8. fc –l
List commands from history
fc –e emacs
Use emacs to edit and reexecute previous command
fc –s <num>
Reexecute command number <num>
fc –s <old_string> =
<new_string>
<num>
Reexecute command number <num> after changing <old_string> to <new_string>

9. dirs - display directory stack
pushd - push a directory on to stack (and go there)
popd - pop a directory from the stack (and go there)

10. Scheduler
decides which processes to run and for how long
uses preemptive multitasking – system decides
(cooperative is the other choice – process “yields”)
Memory manager
virtual memory
system looks like it has more actual memory
pages, page tables
Magic number
embedded near beginning of file – indicates file type
file command uses it to identify type
fork() system call
see fork.c example

11. Data Structure in RAM
Contains info about the following:
PID
PPID (parent)
Real and effective UID and GID
Process state
Location of its code, data, stack and user area
List of all pending signals

12. init - last step in boot process (creates id “1”)
fork(), exec() - spawn new processes
(see fork.c and doexec.c examples)
getty - create terminal session (mingetty)
login - login a user
Modes
User - “normal” user
kernel - root

13. Termination status
Normal - process runs to normal completion
Abnormal - terminated externally (ex: kill -9)
wait() - “C” system call
- parent suspends
… waits for status of child to change
- see waitpid.c example
Zombie process - terminated, but still in process table
- exists so parent can read exit code
- can’t kill it with kill command (see zombie.c)
Orphan process - parent terminated (intentional or not)
- init process becomes parent (see orphan.c)

14. Idle Runnable / Ready Running Zombie Sleeping / Blocked Suspended Exit
To see status codes:
ps -o uid,pid,stat,cmd
Codes:
D Uninterruptible sleep (usually IO)
R Running or runnable (on run queue)
S Interruptible sleep
T Stopped
Z Defunct ("zombie") process
Additional info:
< high-priority (not nice to other users)
N low-priority (nice to other users)
L has pages locked into memory (for IO)
s is a session leader
+ is in the foreground process group
Idle
Runnable / Ready
Running
Zombie
Sleeping / Blocked
Suspended
Exit

15. User
Code area - program instructions
Data area - program data
Stack area - program stack (manage function calls)
User area - housekeeping
Kernel area
Process Table
Page Table

16. Multilevel Priority Queue
scheduling algorithm
Process’ s priority
processes get a priority number
ex: ps -o uid,pid,ppid,pri,ni,cmd
Priority computation
Nice value (nice, renice -n)
20 is nice, -20 is not, 0 default
Context switch
save the process state
restore it later

17. Pages (stored in memory)
Region table (inode ptrs, page table ptrs, process #’s, …)
Page table
Modified bit (“dirty bit” – checks for data modification)
Referenced bit (set when referenced, periodically cleared)
Age (LRU – least recently used)
RAM table (paging DS in RAM)
Page daemon (paging mgmt. process)
Swap space (program moved to disk)
Page fault (page not in memory)

18. Delayed Execution crontab run jobs on a schedule
sets up tables for the cron daemon
to open editor: crontab –e at
execute a command at a specific time
output gets mailed to you (via unix mail)

19. Signals and Sockets Assign a signal handler with signal()
Example: timeout.c
Interprocess server/client communication via a socket
Example: server.c and client.c (with makefile)