Linux 进程学习笔记
Linux Process
Processes carry out tasks within the operating system. A program is a set of machine code instructions and data stored in an executable image on disk and is, as such, a passive entity; a process can be thought of as a computer program in action.
State
As a process executes it changes state according to its circumstances. Linux processes have the following states:
- Running
The process is either running (it is the current process in the system) or it is ready to run (it is waiting to be assigned to one of the system’s CPUs).
- Waiting
The process is waiting for an event or for a resource. Linux differentiates between two types of waiting process; interruptible and uninterruptible. Interruptible waiting processes can be interrupted by signals whereas uninterruptible waiting processes are waiting directly on hardware conditions and cannot be interrupted under any circumstances.
- Stopped
The process has been stopped, usually by receiving a signal. A process that is being debugged can be in a stopped state.
- Zombie
This is a halted process which, for some reason, still has a task_struct data structure in the task vector. It is what it sounds like, a dead process.
Identifiers
Every process in the system has a process identifier. The process identifier is not an index into the task vector, it is simply a number. Each process also has User and group identifiers, these are used to control this processes access to the files and devices in the system.
Links
In a Linux system no process is independent of any other process. Every process in the system, except the initial process has a parent process. New processes are not created, they are copied, or rather cloned from previous processes. Every task_struct representing a process keeps pointers to its parent process and to its siblings (those processes with the same parent process) as well as to its own child processes. You can see the family relationship between the running processes in a Linux system using the pstree command:
# pstree -pu
init(1)─┬─auditd(1338)───{auditd}(1339)
├─crond(1495)
├─master(1481)─┬─pickup(1491,postfix)
│ └─qmgr(1492,postfix)
├─mingetty(1521)
├─mingetty(1523)
├─mingetty(1525)
├─mingetty(1527)
├─mingetty(1529)
├─mingetty(1536)
├─rsyslogd(1360)─┬─{rsyslogd}(1361)
│ ├─{rsyslogd}(1362)
│ └─{rsyslogd}(1363)
├─sshd(1401)───sshd(1557)───bash(1561)───pstree(1615)
└─udevd(604)─┬─udevd(1535)
└─udevd(1537)Additionally all of the processes in the system are held in a doubly linked list whose root is the init processes task_struct data structure. This list allows the Linux kernel to look at every process in the system. It needs to do this to provide support for commands such as ps or kill
Times and Timers
The kernel keeps track of a processes creation time as well as the CPU time that it consumes during its lifetime. Each clock tick, the kernel updates the amount of time in jiffies that the current process has spent in system and in user mode. Linux also supports process specific interval timers, processes can use system calls to set up timers to send signals to themselves when the timers expire. These timers can be single-shot or periodic timers.
查看进程
ps - report a snapshot of the current processes
ps [options]
ps displays information about a selection of the active processes. If you want a repetitive update of the selection and the displayed information, use top(1) instead.
This version of ps accepts several kinds of options:
1 UNIX options, which may be grouped and must be preceded by a dash.
2 BSD options, which may be grouped and must not be used with a dash.
3 GNU long options, which are preceded by two dashes.
Options of different types may be freely mixed, but conflicts can appear. There are some synonymous options, which are functionally identical, due to the many standards and ps implementations that this ps is compatible with.
EXAMPLES
To see every process on the system using standard syntax:
ps -e
ps -ef
ps -eF
ps -ely
To see every process on the system using BSD syntax:
ps ax
ps axu
To print a process tree:
ps -ejH
ps axjfa option causes ps to list all processes with a terminal (tty), or to list all processes when used together with the x option.
x option causes ps to list all processes owned by you (same EUID as ps), or to list all processes when used together with the a option.
u output format control option. display user-oriented format.
j BSD job control format
f ASCII-art process hierarchy (forest)
-e Select all processes. Identical to -A.
-f does full-format listing. This option can be combined with many other UNIX-style options to add additional columns. It also causes the command arguments to be printed. When used with -L, the NLWP (number of threads) and LWP (thread ID) columns will be added. See the c option, the format keyword args, and the format keyword comm.
-F extra full format. See the -f option, which -F implies.
-l long format. The -y option is often useful with this.
-y Do not show flags; show rss in place of addr. This option can only be used with -l.
-j jobs format
-H show process hierarchy (forest)
pstree - display a tree of processes
pstree [options] [pid]|[user]
pstree shows running processes as a tree. The tree is rooted at either pid or init if pid is omitted. If a user name is specified, all process trees rooted at processes owned by that user are shown.
-p Show PIDs. PIDs are shown as decimal numbers in parentheses after each process name. -p implicitly disables compaction.
-u Show uid transitions(转变). Whenever the uid of a process differs from the uid of its parent, the new uid is shown in parentheses after the process name.
-a Show command line arguments. If the command line of a process is swapped out, that process is shown in parentheses. -a implicitly disables compaction.
-h Highlight the current process and its ancestors. This is a no-op if the terminal doesn’t support highlighting or if neither the current process nor any of its ancestors are in the subtree being shown.
-H Like -h, but highlight the specified process instead. Unlike with -h, pstree fails when using -H if highlighting is not available.
-n Sort processes with the same ancestor by PID instead of by name.(Numeric sort.)
top - display Linux tasks
top -hv | -abcHimMsS -d delay -n iterations -p pid [, pid …]
The top program provides a dynamic real-time view of a running system. It can display system summary information as well as a list of tasks currently being managed by the Linux kernel.
w - Show who is logged on and what they are doing
w - [husfiV] [user]
w displays information about the users currently on the machine, and their processes. The header shows, in this order, the current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.
The following entries are displayed for each user: login name, the tty name, the remote host, login time, idle time, JCPU, PCPU, and the command line of their current process.
The JCPU time is the time used by all processes attached to the tty. It does not include past background jobs, but does include currently running background jobs.
The PCPU time is the time used by the current process, named in the “what” field.
杀死进程
kill - terminate a process
kill [-s signal|-p] [–] pid…
kill -l [signal]
The command kill sends the specified signal to the specified process or process group. If no signal is specified, the TERM signal is sent. The TERM signal will kill processes which do not catch this signal. For other processes, it may be necessary to use the KILL (9) signal, since this signal cannot be caught.
pid… Specify the list of processes that kill should signal. Each pid can be one of five things:
n where n is larger than 0. The process with pid n will be signaled. 0 All processes in the current process group are signaled. -1 All processes with pid larger than 1 will be signaled. -n where n is larger than 1. All processes in process group n are signaled. When an argument of the form ‘-n’ is given, and it is meant to denote a process group, either the signal must be specified first, or the argument must be preceded by a ‘--’ option, otherwise it will be taken as the signal to send.-s signal Specify the signal to send. The signal may be given as a signal name or number.
-l Print a list of signal names. These are found in /usr/include/linux/signal.h
# kill -l
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX
# kill -l 15
TERM
# kill -l KILL
9
killall - kill processes by name
killall [-Z,–context pattern] [-e,–exact] [-g,–process-group] [-i,–interactive] [-q,–quiet] [-r,–regexp] [-s,–signal signal] [-u,–user user] [-v,–verbose]
[-w,–wait] [-I,–ignore-case] [-V,–version] [–] name …
killall -l
killall sends a signal to all processes running any of the specified commands. If no signal name is specified, SIGTERM is sent.
Signals can be specified either by name (e.g. -HUP or -SIGHUP ) or by number (e.g. -1) or by option -s.
If the command name is not regular expression (option -r) and contains a slash (/), processes executing that particular file will be selected for killing, independent of their name.
killall returns a zero return code if at least one process has been killed for each listed command, or no commands were listed and at least one process matched the -u and -Z search criteria. killall returns non-zero otherwise.
A killall process never kills itself (but may kill other killall processes).
OPTIONS
-e, –exact
Require an exact match for very long names. If a command name is longer than 15 characters, the full name may be unavailable (i.e. it is swapped out). In
this case, killall will kill everything that matches within the first 15 characters. With -e, such entries are skipped. killall prints a message for each
skipped entry if -v is specified in addition to -e,
-I, --ignore-case
Do case insensitive process name match.
-g, --process-group
Kill the process group to which the process belongs. The kill signal is only sent once per group, even if multiple processes belonging to the same process
group were found.
-i, --interactive
Interactively ask for confirmation before killing.
-l, --list
List all known signal names.
-q, --quiet
Do not complain if no processes were killed.
-r, --regexp
Interpret process name pattern as an extended regular expression.
-s, --signal
Send this signal instead of SIGTERM.
-u, --user
Kill only processes the specified user owns. Command names are optional.
-v, --verbose
Report if the signal was successfully sent.
-V, --version
Display version information.
-w, --wait
Wait for all killed processes to die. killall checks once per second if any of the killed processes still exist and only returns if none are left. Note that
killall may wait forever if the signal was ignored, had no effect, or if the process stays in zombie state.
-Z, --context
(SELinux Only) Specify security context: kill only processes having security context that match with given expended regular expression pattern. Must precede
other arguments on the command line. Command names are optional.pgrep, pkill - look up or signal processes based on name and other attributes
SYNOPSIS
pgrep [-flvx] [-d delimiter] [-n|-o] [-P ppid,...] [-g pgrp,...]
[-s sid,...] [-u euid,...] [-U uid,...] [-G gid,...]
[-t term,...] [pattern]
pkill [-signal] [-fvx] [-n|-o] [-P ppid,...] [-g pgrp,...]
[-s sid,...] [-u euid,...] [-U uid,...] [-G gid,...]
[-t term,...] [pattern]DESCRIPTION
pgrep looks through the currently running processes and lists the process IDs which matches the selection criteria to stdout. All the criteria have to match. For example,
pgrep -u root sshd
will only list the processes called sshd AND owned by root. On the other hand,
pgrep -u root,daemon
will list the processes owned by root OR daemon.
pkill will send the specified signal (by default SIGTERM) to each process instead of listing them on stdout.OPTIONS
-d delimiter
Sets the string used to delimit each process ID in the output (by default a newline). (pgrep only.)
-f The pattern is normally only matched against the process name. When -f is set, the full command line is used.
-g pgrp,...
Only match processes in the process group IDs listed. Process group 0 is translated into pgrep’s or pkill’s own process group.
-G gid,...
Only match processes whose real group ID is listed. Either the numerical or symbolical value may be used.
-l List the process name as well as the process ID. (pgrep only.)
-n Select only the newest (most recently started) of the matching processes.
-o Select only the oldest (least recently started) of the matching processes.
-P ppid,...
Only match processes whose parent process ID is listed.
-s sid,...
Only match processes whose process session ID is listed. Session ID 0 is translated into pgrep’s or pkill’s own session ID.
-t term,...
Only match processes whose controlling terminal is listed. The terminal name should be specified without the "/dev/" prefix.
-u euid,...
Only match processes whose effective user ID is listed. Either the numerical or symbolical value may be used.
-U uid,...
Only match processes whose real user ID is listed. Either the numerical or symbolical value may be used.
-v Negates the matching.
-x Only match processes whose name (or command line if -f is specified) exactly match the pattern.
-signal
Defines the signal to send to each matched process. Either the numeric or the symbolic signal name can be used. (pkill only.)OPERANDS
pattern
Specifies an Extended Regular Expression for matching against the process names or command lines.
EXAMPLES
Example 1: Find the process ID of the named daemon:
unix$ pgrep -u root named
Example 2: Make syslog reread its configuration file:
unix$ pkill -HUP syslogd
Example 3: Give detailed information on all xterm processes:
unix$ ps -fp $(pgrep -d, -x xterm)
Example 4: Make all netscape processes run nicer:
unix$ renice +4 ‘pgrep netscape‘EXIT STATUS
0 One or more processes matched the criteria.
1 No processes matched.
2 Syntax error in the command line.
3 Fatal error: out of memory etc.NOTES
The process name used for matching is limited to the 15 characters present in the output of /proc/pid/stat. Use the -f option to match against the complete command line, /proc/pid/cmdline.
The running pgrep or pkill process will never report itself as a match.通过 -t 选项剔除某个用户：
# pkill -9 -t pts/1进程优先级
查看进程优先级
ps 命令的 -el 选项可查看进程优先级：
# ps -el
F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
4 S 0 1 0 0 80 0 - 726 - ? 00:00:01 init
1 S 0 2 0 0 80 0 - 0 - ? 00:00:00 kthreadd
1 S 0 3 2 0 -40 - - 0 - ? 00:00:00 migration/0
1 S 0 4 2 0 80 0 - 0 - ? 00:00:00 ksoftirqd/0
1 S 0 5 2 0 -40 - - 0 - ? 00:00:00 stopper/0
1 S 0 6 2 0 -40 - - 0 - ? 00:00:00 watchdog/0
1 S 0 7 2 0 -40 - - 0 - ? 00:00:00 migration/1
1 S 0 8 2 0 -40 - - 0 - ? 00:00:00 stopper/1
1 S 0 9 2 0 80 0 - 0 - ? 00:00:00 ksoftirqd/1
1 S 0 10 2 0 -40 - - 0 - ? 00:00:00 watchdog/1
5 S 0 11 2 0 80 0 - 0 - ? 00:00:00 events/0
1 S 0 12 2 0 80 0 - 0 - ? 00:00:03 events/1
1 S 0 13 2 0 80 0 - 0 - ? 00:00:00 events/0
1 S 0 14 2 0 80 0 - 0 - ? 00:00:00 events/1
1 S 0 15 2 0 80 0 - 0 - ? 00:00:00 events_long/0
1 S 0 16 2 0 80 0 - 0 - ? 00:00:00 events_long/1
1 S 0 17 2 0 80 0 - 0 - ? 00:00:00 events_power_ef
1 S 0 18 2 0 80 0 - 0 - ? 00:00:00 events_power_efPRI(Priority) 和 NI(Niceness) 都表示优先级，数字越小表示该进程的优先级越高，用户不能修改 PRI，只能修改 NI 的值。
PRI (最终值) = PRI(原始值) + NI
NI 值的范围是 -20 到 19，普通用户调整 NI 的范围是 0 到 19，而且只能调高 NI 不能减低。
只有 root 用户才能设定进程 NI 为负值，而且可以调整任何用户的进程。
修改进程优先级
nice - run a program with modified scheduling priority
nice [OPTION] [COMMAND [ARG]…]
Run COMMAND with an adjusted niceness, which affects process scheduling. With no COMMAND, print the current niceness. Nicenesses range from -20 (most favorable scheduling) to 19 (least favorable).
-n, --adjustment=N
add integer N to the niceness (default 10)NOTE: your shell may have its own version of nice, which usually supersedes the version described here. Please refer to your shell’s documentation for details about the options it supports.
后台进程管理
jobs
fg
bg
ctrl+z
& - 终端关闭，进程终止
nohup COMMAND & - 终端关闭，进程后台继续运行，程序的输出到 nohup.out 文件