kill -9 和 pkill 是在类 Unix 系统中用来终止进程的两个不同命令，它们之间有以下主要区别：
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信号不同：
kill -9：发送SIGKILL信号给指定的进程。SIGKILL（信号值为 9）是一个强制杀死进程的信号，不能被进程捕获或忽略，进程将立即终止。pkill：可以发送多种信号给进程，SIGKILL只是其中之一。使用pkill时，可以通过-s或--signal选项指定要发送的信号。
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目标选择方式不同：
kill -9：通常需要指定要杀死的进程的 PID（进程 ID），例如kill -9 1234。pkill：通过进程名或其他属性来选择要杀死的进程，例如pkill -9 nginx会向所有名为nginx的进程发送SIGKILL信号。
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使用范围：
kill -9：只能杀死单个指定的进程。pkill：可以杀死所有匹配特定条件的进程，这使得pkill更适合批量操作。
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适用场景：
kill -9：由于其强制杀死进程的特性，通常作为最后的手段使用，当其他信号（如SIGTERM）无法终止进程时。pkill：更适合需要同时终止多个相同名称或属性的进程的场景。
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命令选项：
kill -9：选项较少，主要用来发送SIGKILL信号。pkill：有更多的选项，可以指定信号、匹配条件等。
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安全性：
kill -9：由于不能被进程捕获或忽略，使用时需要谨慎，以避免可能的数据丢失或不一致。pkill：虽然也可以发送SIGKILL，但由于其选择性更强，可以更精确地控制要杀死的进程集合。
总结来说，kill -9 是一个简单直接的命令，用于强制杀死指定的单个进程，而 pkill 提供了更多的灵活性和选择性，可以发送不同的信号并针对一组进程执行操作。在实际使用中，应根据具体需求和场景选择合适的命令。
pkill -help
Usage:
pkill [options] <pattern>
Options:
-<sig>, --signal <sig> signal to send (either number or name)
-e, --echo display what is killed
-c, --count count of matching processes
-f, --full use full process name to match
-g, --pgroup <PGID,...> match listed process group IDs
-G, --group <GID,...> match real group IDs
-n, --newest select most recently started
-o, --oldest select least recently started
-P, --parent <PPID,...> match only child processes of the given parent
-s, --session <SID,...> match session IDs
-t, --terminal <tty,...> match by controlling terminal
-u, --euid <ID,...> match by effective IDs
-U, --uid <ID,...> match by real IDs
-x, --exact match exactly with the command name
-F, --pidfile <file> read PIDs from file
-L, --logpidfile fail if PID file is not locked
--ns <PID> match the processes that belong to the same
namespace as <pid>
--nslist <ns,...> list which namespaces will be considered for
the --ns option.
Available namespaces: ipc, mnt, net, pid, user, uts
-h, --help display this help and exit
-V, --version output version information and exit
For more details see pgrep(1).
KILL(1) User Commands KILL(1)
NAME
kill - terminate a process
SYNOPSIS
kill [-s signal|-p] [-q sigval] [-a] [--] pid...
kill -l [signal]
DESCRIPTION
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 pro‐
cesses 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.
Most modern shells have a builtin kill function, with a usage rather similar to that of the command described here. The '-a' and '-p' options, and the possibility to spec‐
ify processes by command name are a local extension.
If sig is 0, then no signal is sent, but error checking is still performed.
OPTIONS
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.
commandname
All processes invoked using that name will be signaled.
-s, --signal signal
Specify the signal to send. The signal may be given as a signal name or number.
-l, --list [signal]
Print a list of signal names, or convert signal given as argument to a name. The signals are found in /usr/include/linux/signal.h
-L, --table
Similar to -l, but will print signal names and their corresponding numbers.
-a, --all
Do not restrict the commandname-to-pid conversion to processes with the same uid as the present process.
-p, --pid
Specify that kill should only print the process id (pid) of the named processes, and not send any signals.
-q, --queue sigval
Use sigqueue(2) rather than kill(2) and the sigval argument is used to specify an integer to be sent with the signal. If the receiving process has installed a han‐
dler for this signal using the SA_SIGINFO flag to sigaction(2), then it can obtain this data via the si_value field of the siginfo_t structure.