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Solaris is a multitasking environment in which a number of programs run at the same time. This means that many users can be active on the system at the same time, running many jobs (processes) simultaneously. Each Solaris program can start and stop multiple processes while it is running, but only one job is active per processor at any given time while the other jobs wait in a job queue. Because each process takes its turn running in very short time slices (much less than a second each), multitasking operating systems give the appearance that multiple processes are running at the same time. A parent process forks a child process, which, in turn, can fork other processes.
A process is an instance of a running program. It can be any task that has an address space, executes its own piece of code, and has a unique process ID (PID). A process can create another process called a child process Any process that creates the child process is called the parent process. This creation of new processes from existing parent processes is called forking (after the C function called fork()). Most processes in the system are created by fork system calls. A system call causes the current process to be split into two processes: a parent process and a child process. The child process continues to execute on the CPU until it completes. On completion, the child process returns to the system any resources that it used during its execution. While the child process is running, the parent process either waits for the child process to complete or continues to execute. If the parent process continues to execute, it periodically checks for the completion of the child process.
A process is an instance of a running program.
Process has several attributes:
Running multiple processes has an impact on system performance because the processes consume system resources, such as memory and processor time, and some processes may even cause the system to hang. Managing processes becomes important in a multi-user environment such as Solaris. Managing processes involves monitoring the processes, finding the resource usage, finding the parent processes that have created child processes, assigning priority for processes, and terminating processes.
A process can change its state during its lifetime, often multiople times. For example, if a parent process waits for the child process to complete execution, the parent process puts itself in sleep state. Such a change from run state to sleep state is known as a context switch.
During its lifetime a process can exist in four states:
Init is the first genuine user process the system creates. All other processes on the system are created by forking the Init process. If the process is in the Run state, it means that the process is running on the CPU. In the Sleep state, the process waits for a child process to complete, or waits for a resource. Zombie is the phase in which the child process terminates and is not removed from the system until the parent process acknowledges the death of the child process. In this case, the child process is said to be in a Zombie state.
There are several Solaris command that help to monitor processes
To view the state of a process, use the ps and pgrep commands. The ps command, without any options, lists the process ID (PID), associated terminal (TTY), the cumulative execution time (TIME), and the command that generated the process (CMD)
$ ps PID TTY TIME CMD 6213 pts/5 0:00 sh 6233 pts/5 0:00 psThe ps -a command lists the most frequently requested processes. It displays only the processes that are associated with the terminal from which the ps command is issued. To list all the processes currently running on a system, use the -A option with the ps command.
The ps el command displays a full listing of all the processes running on the system
$ps -el F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD 19 T 0 0 0 0 0 SY ? 0 ? 0:15 sched 8 S 0 1 0 0 40 20 ? 151 ? ? 0:00 init 19 S 0 2 0 0 0 SY ? 0 ? ? 0:00 pageout 19 S 0 3 0 0 0 SY ? 0 ? ? 10:43 fsflush 8 S 0 314 1 0 40 20 ? 222 ? ? 0:00 sac 8 S 0 229 1 0 40 20 ? 130 ? ? 0:00 utmpd 8 S 0 180 1 0 40 20 ? 596 ? ? 0:01 automoun 8 S 0 52 1 0 40 20 ? 283 ? ? 0:00 sysevent 8 S 0 59 1 0 40 20 ? 338 ? ? 0:01 picld 8 S 0 111 1 0 40 20 ? 208 ? ? 0:02 in.route 8 S 0 118 1 0 40 20 ? 242 ? ? 0:00 in.ndpd 8 S 0 156 1 0 40 20 ? 311 ? ? 0:00 inetd 8 S 0 188 1 0 40 20 ? 417 ? ? 0:00 syslogd 8 S 0 133 1 0 40 20 ? 308 ? ? 0:00 rpcbind 8 S 0 170 1 0 40 20 ? 289 ? ? 0:00 lockd 8 S 25 420 1 0 40 20 ? 535 ? ? 0:00 sendmail 8 S 1 169 1 0 40 20 ? 318 ? ? 0:00 statd 8 S 0 218 1 0 40 20 ? 176 ? ? 0:00 powerd 8 S 0 195 1 0 40 20 ? 284 ? ? 0:00 cron 8 S 0 210 1 0 40 20 ? 387 ? ? 0:01 nscd 8 S 0 4972 4971 0 80 30 ? 520 ? ? 0:00 dtscreen
F— Flags associated with the process.
S— The state of the process.If state is Z this is a zombie process. Pretty common for Websphere and other semi-debugged applications. For further information on the fields, view man pages for the ps command.
UID— The user ID.
PID— Each process has an associated ID. You can use this ID to determine the state of a specific process.
PPID— The parent process ID.
C— Processor utilization.
PRI— The set scheduling parameters for a process.
NI— The nice value displays the assigned priority to the process.
ADDR— The memory address of the process.
SZ— The total number of pages in the process, in virtual memory, including all mapped files and devices.
WCHAN— The address of an event for which the process is sleeping.
TTY— The terminal from which the process originated. System processes have a ? in this field.
TIME— The processor utilization time.
CMD— The command that has spawned the process.
For more information see Unix ps command
The pgrep command displays a list of the process IDs of active processes on the system that match the pattern specified in the command line. The pgrep command functionally combines the ps command with the grep command. The syntax for the pgrep command is as follows:
pgrep [-option] pattern
|- l||long listings (name of the profess and its PID)|
|-g pgrplist||Matches the processes with the process group ID.|
Matches the active processes with the group ID(s) specified in the command line. For example, if you are searching for processes running with the group ID sysman, specify the command pgrep G sysman.
Specifies a delimiter for separating PIDs.
Matches the most recent process.
The processes are matched with the parent process ID in the listing.
The processes are matched with the session ID in the list.
Matches the terminal on which the process is running.
Matches processes with the effective used ID in the list. The effective uid is the uid of the executable file when the SUID of the file is set.
Matches processes with the real uid in the list. The real uid is the uid that the user uses when starting a task or a process.
Matches all processes except those that meet the specified criteria in the command line.
Matches pattern against full arguments rather than the name of the executable file.
Matches the processes that exactly match the specified pattern.
The following example displays the process ID for the process sh:
$ pgrep sh 3 8027 307 765 762 6488 7970 8147 8150
The following command displays the process ID of all those processes matching the in pattern:
$ pgrep in* 1 59 111 118 156The pgrep command with the l option displays the name of the processes, which contains the string in along with their PIDs.
$ pgrep -l in 1 init 111 in.routed 118 in.ndpd 156 inetd 133 rpcbind
The following command displays the processes owned by user James:
$ pgrep -u james 1459 1464 $
You can combine options. In the following example, both the l and the u options are used together with the pgrep command to display the names of all the processes run by user James, along with his process ID.
$ pgrep -l -u james 1459 sh 1464 csh
The -d option is used to specify a delimiter for separating PIDs when more than one process ID is tested in the output of the pgrep command. The following example uses delimiters for the listed processes for the user James.
$ pgrep d";" u james 951; 1042; 1051
You can specify more than one user ID by using a comma (,) as a field separator.
Use the kill and the pkill commands to terminate a process. These commands send the appropriate signal to the intended processes to terminate them. A signal notifies a process that an event has occurred. The event could be raised because of issues with the hardware or software, a change in the system date, a change in the system state, and so forth. An inter-process communication takes place because one process sends a signal to another process to instruct the latter to act in a certain manner.
The kill command enables the user to kill the process. Only a superuser can kill a process owned by others. The kill command sends a signal to a process, which is used to terminate it. The syntax for the kill command is
# kill <signal> <process ID>
To kill a process, you should know its process ID. To find the process ID, you may use the following command:
ps ef | grep <process name>
Even though many signals are available, signal 15 and 9 are the ones that are generally used with the kill command.
Some processes still exist even after a SIGTERM signal. A process might still be alive for the following reasons:
The process is hung.
The process is waiting for some other process to execute.
The process is in the state of Zombie. Note that the process in the Zombie state is not alive and does not use any resources or accomplish any work. However, it is not allowed to die until the parent process acknowledges the exit call.
The process is waiting for some unavailable resources. The resources may be network resources or access to a device.
The kill command, without any signal, issues the SIGTERM (signal 15), by default.
The following syntax sends signal 15 to the process with a process ID of 1305.
# kill 1305
The following example illustrates using the kill command to send signal 9 to kill three different processes:
$ kill 9 3012 3019 3510 $ 3510 killed $ 3019 killed $ 3012 killed
Any number preceded by a minus (-) sign in the <PID> field represents a process group ID. In the following example, the 9 signal is sent to the process with PID 1039 and all the processes with the process group 117.
#kill 9 1039 117
The pkill command terminates the displayed processes that match the pattern specified. The pattern is a regular expression that is used to specify processes based on the program name. By default the pkill command sends the SIGTERM (signal 15) to the matching processes. The command syntax for the pkill command is as follows:
pkill [-option] pattern.
The pkill command takes any signal other than signal 15 (SIGKILL). The following command sends a SIGKILL signal to the processes owned by user joeuser:
# pkill 9 u joeuser
The Bourne shell does not provide job control. Only The Korn shell (ksh) and the C shell (csh) both allow for job control.
Commands such as vi are foreground processes—they read input from the keyboard and display output to the terminal. Foreground processes maintain control of the terminal, and the user cannot do anything else in that terminal window until the execution of that command is complete.
Some processes are not interactive and don't need to run in the foreground. These are referred to as background processes or jobs. A background process gets detached from the terminal, freeing up the terminal while it is running. When a user decides to run a process in the background, you must arrange for the process to get its input from another source. In addition, you need to arrange for the process to output to a device other than the terminal, such as a file.
To run a process in the background, enter an & (ampersand) after the command:
# find . -name core -print &After typing in this command, you're returned to a command prompt. The find command executes in the background. One problem, however, is the standard output is still on your terminal. In other words, as the find command executes, the results still are displayed on your screen, which can become quite annoying. It's best to redirect the output to a file, as follows:
# find . -name core -print > /tmp/results & After you put the find command in the background, the system displays two numbers associated with that process—the job number and the process ID number (PID) as follows:
 14919You use this job number to control background processes.
The shell maintains a table containing information about processes that are currently in the background. This is referred to as the jobs table. The jobs table is unique to the user, and each user has his own jobs table. Furthermore, the jobs table contains only entries for jobs that are running in your current shell. If you start a new shell, the jobs table for the new shell is empty. Each job in the table is assigned a number that is unique to that user only. In other words, two users can each have a job numbered 1. Don't confuse this job number with a process ID number; remember, process IDs are unique, and no two share the same number. Any jobs that the user has placed in the background are displayed here by typing in the jobs command, as follows:
# jobsThe system responds with this:
 + Running find / -name bill -print > /tmp/results3 &
 - Running find / -name junk -print > /tmp/results2 &
 Running find / -name core -print > /tmp/results1 &The jobs table contains the following information:
A numeric value for each job
A + (plus) symbol to designate the current job that user commands will operate on
A - (minus) symbol to designate the next job that the user commands will operate on
The status of the job
The name of the job
Each job in the job table has one of the following states:
Running—An active job
Stopped—A job that has been suspended
Terminated—A job that has been killed
Done—A completed job
When the job finishes, the following is displayed on your terminal:
 + Done find / -name core -print > /tmp/results &Note the job number of 1 and the status of Done.
If you want to terminate a job, use the kill command followed by a % (percent sign) and then the job number, as follows:
# kill %1CAUTION
Pay special attention to the use of the % (percent) symbol—it's absolutely required. Without it, you could kill the wrong process and potentially crash the system. Get familiar with the kill command in the next section of this chapter before you use it.
If you do not enter a number following the % sign, the command acts upon the current job entry listed in the jobs table. For this example, you are going to kill job number 1, as follows:
# kill %1The following message is displayed indicating successful termination:
 + Terminated find / -name core -print > /tmp/results &You can also bring a job back into the foreground with the fg command. Typing fg with no arguments brings the current job (the job with the + sign next to it in the jobs table) into the foreground. You can also specify the job by typing fg %<job number>, as follows:
# fg %2This brings job 2 back into the foreground on your terminal.
Signals are software interrupts. For example, the kill command is used to send a signal to a process. System administrators most often use the signals SIGHUP, SIGKILL, SIGSTOP, and SIGTERM. The SIGHUP signal is used by some utilities as a way to notify the process to do something, such as re-read its configuration file. The SIGHUP signal is also sent to a process if the remote connection is lost or hangs up. The SIGKILL signal is used to abort a process, and the SIGSTOP signal is used to pause a process. The SIGTERM signal is the default signal sent to processes by commands such as kill and pkill when no signal is specified. Exam Alert
Don't worry about remembering all of the signals listed; just be familiar with the more common signals, such as SIGHUP, SIGKILL, SIGSTOP, and SIGTERM.
The most common signals an administrator is likely to encounter are signals with numric codes below 16
Obtain a list of the signals type kill -l
The kill command sends a terminate signal (signal 15) to the process, and the process is terminated. Signal 15, which is the default when no options are used with the kill command, is a gentle kill that allows a process to perform cleanup work before terminating. Signal 9, on the other hand, is called a sure, unconditional kill because it cannot be caught or ignored by a process. If the process is still around after a kill -9, either it is hung up in the Unix kernel, waiting for an event such as disk I/O to complete, or you are not the owner of the process.
The kill command is routinely used to send signals to a process. You can kill any process you own, and the superuser can kill all processes in the system except those that have process IDs 0, 1, 2, 3, and 4. The kill command is poorly named because not every signal sent by it is used to kill a process. This command gets its name from its most common use—terminating a process with the kill -15 signal.
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