Linux System Administration

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1 System Processes Objective At the conclusion of this module, the student will be able to: Describe and define a process Identify a process ID, the parent process and the child process Learn the PID for a process Kill a process Discover who is logged in System Processes 2 1

2 chown chown changes the user and/or group ownership of each given FILE to NEW-OWNER or to the user and group of an existing reference file chown [OPTION].. {NEW-OWNER --reference=ref_file} FILE... OPTIONS -c, --changes Verbosely describe only files whose ownership actually changes. -f, --silent, --quiet Do not print error messages about files whose ownership cannot be changed. -v, --verbose Verbosely describe ownership changes. -R, --recursive Recursively change ownership of directories and their contents. System Processes 3 chown If used, NEW-OWNER specifies the new owner and/or group as follows [OWNER] [ [:] [GROUP] ] Where: OWNER If only an OWNER (a user name or numeric user id) is given, that user is made the owner of each given file, and the files group is not changed. OWNER:GROUP If the OWNER is followed by a colon and a GROUP (a group name or numeric group id), with no spaces between them, the group ownership of the files is changed as well OWNER: If a colon but no group name follows OWNER, that user is made the owner of the files and the group of the files is changed to OWNERs login group. :GROUP If the colon and following GROUP are given, but the owner is omitted, only the group of the files is changed; in this case, chown performs the same function as chgrp. System Processes 4 2

3 chown Example System Processes 5 System Processes UNIX manages tasks using processes A process consists of an address space and a set of data structures in the kernel to keep track of that process The address space is a section of memory that contains the code to execute as well as the process stack Each program creates a process which is assigned a unique process identification number (PID) A process can spawn a subprocess, thus creating a process hierarchy with parent / child relationships Some simple commands, such as cd, are executed by the shell itself and do not create a separate process System Processes 6 3

4 Processes and the kernel The kernel must keep track of the following data for each process on the system: the address space map, the current status of the process, the execution priority of the process, the resource usage of the process, the current signal mask, the owner of the process. System Processes 7 Attributes of a Process A process has certain attributes that directly affect execution, these include: PID The PID stands for the process identification This is a unique number that defines the process within the kernel PPID This is the processes Parent PID, the creator of the process UID The User ID number of the user that owns this process EUID The effective User ID of the process GID The Group ID of the user that owns this process EGID The effective Group User ID that owns this process priority The priority under which this process runs System Processes 8 4

5 Kernel Allocation for Processes Upon boot, two processes started sched (scheduler)(pid 0) init (initialization)(pid 1) which manages other processes System Processes 9 ps [options] The ps options change under different flavors Linux uses the BSD options HP-UX uses the System V version Solaris and AIX make both versions available The two common ones that we will use are variations of ps aux and ps ef ps Options -a select all with a tty except session leaders -u select by effective user ID (supports names) -x select processes without controlling ttys -e select all processes -f does full listing System Processes 10 5

6 Viewing Running Processes To view a process you use the ps command. ps -l F S UID PID PPID C PRI NI P SZ:RSS WCHAN TTY TIME COMD 30 S * 66: f10 ttyq6 0:00 rlogind 30 S * 129: f10 ttyq6 0:00 zwgc 30 S * 85: ttyq6 0:00 csh 30 S * 86: c ttyq6 0:00 login.kr 30 S * 86: ttyq6 0:00 csh 30 R :171 ttyq6 0:01 ps System Processes 11 ps Fields The F field. This is the flag field. uses hexadecimal values which are added to show the value of the flag bits for the process For a normal user process this will be 30, meaning it is loaded into memory. The S field. The S field is the state of the process, the two most common values are S for Sleeping and R for Running An important value to look for is X, which means the process is waiting for memory to become available When you see this frequently on your system you are out of memory. UID field. The UID field shows the User ID (UID) of the process owner For many processes this is 0 because they are run setuid. PID field. The PID shows the Process ID of each process This value should be unique Generally PID are allocated lowest to highest, but wrap at some point This value is necessary to send a signal to a process such as the KILL signal System Processes 12 6

7 ps Fields PPID field. This refers to the Parent Process ID identifies the parent process that started the process Using this allows us to trace the sequence of process creation that took place PRI field. This stands for priority field. The lower the value the higher the priority value This refers to the process NICE value will range form 0 to 39 The default is 20, as a process uses the CPU the system will raise the nice value This value is used by the scheduler to compute the next process to get the cpu. The P flag. This is the processor flag On the SGI this refers to the processor the process is running on System Processes 13 ps Fields SZ field This refers to the SIZE field the total number of pages in the process Each page is 4096 bytes Use the sort command as the pipe output to sort by size or PID to sort by SZ field use the command ps -el sort +9 RSS field. This refers to Resident Set Size and refers to the pages in memory TTY field. This is the terminal assigned to your process On SGI based systems tty's with the letter q in them are psuedo, or network, tty's Time field The cumulative execution time of the process in minutes and seconds COMD field The command that was executed System Processes 14 7

8 ps and grep Using ps with grep is a useful way to extract information on a particular process For example, the command: ps -ef grep bash would return process information on bash We can keep track of a particular process that is running at the background System Processes 15 Types of Processes Daemon processes that exist for a specific purpose (lpsched daemon) exists for the sole purpose of handling print jobs May run in the background until needed or moved to the foreground Parent process which spawns another process following boot-up, a process called init daemon is invoked every process, except init, has a parent process Child process spawned by another process when working in a terminal window, the terminal s PID is the parent process ID (PPID) of any commands issued in the terminal these commands are child processes System Processes 16 8

9 Types of Processes Runnable The process is running or is in the queue for the CPU resources. Sleeping The process is inactive, usually for a brief period. Idle The process is inactive for an extended period. Swapped The process has been swapped to disk to free memory. This process requires time to restart System Processes 17 Types of Processes Blocked The process is waiting for I/O to finish, or for another un-interruptible system operation to take place Traced The process has been suspended or is being traced. Orphan A child process that continues to run after the parent process is killed system passes the orphan process to init it then becomes the parent process and is terminated System Processes 18 9

10 Types of Processes Zombie (defunct process) a process that has died or becomes lost in the system a child process does not return to the parent process with its output the process continues to have a PID and the status will be marked as Z with the ps command You cannot kill Zombies as they are already dead The only way to kill a zombie is to reboot Nice A process is nice if its priority has been set lower than the default System Processes 19 Terminating a Process The kill command is used to send signals to processes You must be the owner of a process, or root, to send it a signal Signals may be specified by name or number (1=HUP, KILL=9, TERM=15) If no signal is specified, TERM is assumed System Processes 20 10

11 kill syntax Option Description -HUP PID or -1 PID Tells a daemon process that its configuration information has changed and that it should re-read its configuration files -TERM PID -15 PID Tells process that it should terminate in an orderly manner -9 PID Terminates a process immediately, allowing no time for the process to clean up System Processes 21 Learning Which Users on the System To find out who is logged in who Jun 25 15:10 13 id=si term=0 exit=0 system boot Jun 25 15:10 run-level 3 Jun 25 15:10 last=s Jun 25 15: id=l3 term=0 exit=0 root + tty1 Jun 26 05:14 old 1838 root + tty2 Jun 26 05:31 old 1839 root + pts/0 Jun 26 12: (:0.0) Also finger Login Name Tty Idle Login Time Office Office Phone root root tty1 1d Jun 26 05:14 root root tty2 2d Jun 26 05:31 root root pts/0 Jun 26 12:23 (:0.0) System Processes 22 11

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