Sec. 2 Processes Flashcards
a program is a ……?
set of instructions, along with any internal data used while carrying in the instructions out.
a program may also use ….?
external data
what is a process?
a process is an executing program and associated resources .
- including :
- enviorment open files
- signal handlers
- etc…
when it comes to an everything is shared situtation with processes one speaks of …..?
multi-threaded process
In linux each thread of execution is considered …..?
individually
describe what a process is:
A process is an instance of an executing program .
every process has a ….?
process id or pid, a ppid or parent process id and a pgid (process group id)
every process also has ……?
- program code
- data
- variables,
- file descriptors
- and an evironment
init is usually the first _______ ?
process run ona system.
if the parent process dies before the child the ppid of the child is set to …..?
1
the child process which dies before its parent is known as a ….?
zombie process
Zombie processes have released all of their resoures and remain only to …..?
convey their exit status
processes are controlled by …..?
scheduling
Scheduling of processes is completely ….?
preemptive
All process have certain attributes . what are they?
- the program being executed
- context (state)
- permissions
- associated resources
every process is executing some …….?
program
explain what the context of a process is .
at any given moment , a process may taek a snapshot of itself by trapping the state of its CPU registers, where it is executing in the program, what is in the process’ memory and other information. this is the processs’ context
when a process started it is isolated in it own ______ ______ to protect is from other processes .
user space
do processes have direct acces to hardware?
no
Hardware is managed by the ……?
kernel
a process will have to use (what?) to indirectly access hardware
system calls
system calls are the fundamental interface between (what?) and the (what?)
application, kernel
ulimit
ulimit is a built in bash command that displays or resets a number of resource limits associated with processes running under the shell.
using ulimit how would see what is running?
ulimit -a
when using ulimit there are two types of limits . what are they?
- hard
and
- soft
define the hard limit:
- the hard limit:
- the maximum value , set only by the root user, that a user can raise the resource limit to .
- example :
- ulimit -H -n
define the soft limit:
-
soft limit:
- the current limiting value, which the user can modify, but cannot exeed the hard limit.
what is the syntax of the command ulimit
ulimit [option] [limit]
changes made with ulimit only affect the current shell if i want to make the changes effective for all users I would need to modify what file?
/etc/security/limits.conf
processes can be one of several …….?
states
define the process state : running
-
process state: running
- the process is either currently executing on a CPU or CPU core or sittingin thr run queue, eargerly awaiting a new time slice.
- it will resume running when the scheduler decides it is now deserving to occupy the CPU, or another CPU becomes idle
du
- Name:
- du —- estimate file space usage
- synopsis:
- du – [option] … [file] …
- Discription:
- summarize disk usage of the set of files, recursively for directories .
du –all
writes count ofr all files , not just directories.
du –apparent-size
print apparent sizes , rather that disk usage; although the apparent size is usually smaller, it may be larger du to holes in files….
du –c , –total
will produce a grand total of the disk summary usage
du –d; –max-dept=N
print the total for a directory only if if is N or fewer levels below teh comand line arguement.
–max-depth=0 is the same as –summarize
–maxdepth=1: Just go down one level from / and sum up everything recursively underneath in the tree.
du -h ; –human-readable
du’s output will print sizes in human readable format e.g. , 1k ,234 M…
du –inodes
will list inode usage instead of block usuage
du –time
show time of the last modification of any file in the directory, or any of it subdirectories
du –X , –exclude-from=File
exclude files that match any pattern in File
du -x ; –one-file-system
skip directories on different file systems
-x Stay on one filesystem ; don’t look at directories that are not on the / partition. In this case that means ignore: /dev /proc /run /sys
because these are pseudo-filesystems(/dev /proc /run /sys) which exist in memory only; they are just empty mount points when the system is not running.
To obtain a full list of directories under / along with their size:
$ sudo du –max-depth=1 -hx /
ulimit -S
-S , specifies the soft limit
ulimit -H
-H , specifies the hard limit
ps
- Name: ps
- ps - [options]
- Discription:
- ps displays information about a selection of the active processes
ps -e
see every process on the system using standard syntax
by default , ps selects all processes with the same effective _________ as the current user and associated with the same terminal as the invoker. .
user ID
ps works by reading the _____________ ?
virtual files in /proc
ps -o
option : cgroup
display control groups to which the process belongs
ps -o
option : cgroup
display control groups to which the process belongs
ps -o
option : cgname
display name of control groups to which the process belongs
ps -o
option : c
processor utilization. Currently , this is teh integer value of the percent usage over the lifetime of the process
ps -o
option : blocked
mask of the blocked signals. according to the width of teh field, a 32 or 64-bit mask in hexadecimal format is displayed
