11.观察和管理进程.pptVIP

总结和实验 摘要和实验 进程是在内存中的指令集 进程通过ps,kill,top,gnome-system-monitor命令来管理 挂起作业用Ctrl-z,管理作业用fg,bg命令 crontab exit状态 test If 语法 注：全部的实验和练习题也可以直接从我们的网站上下载 Objectives Upon completion of this unit, you should be able to: Explain what a process is Describe how to manage processes Use job control tools Schedule recurring jobs Employ decision making constructs in shell scripts What is a Process? A process is a set of instructions loaded into memory Numeric Process ID (PID) used for identification UID, GID and SELinux context determines filesystem access Normally inherited from the executing user Listing Processes View Process information with ps Shows processes from the current terminal by default a includes processes on all terminals x includes processes not attached to terminals u prints process owner information f prints process parentage o PROPERTY1,PROPERTY2,... prints custom information: pid, comm, %cpu, %mem, state, tty, euser, ruser, etc. Example: ps?axo?pid,%cpu,comm Finding Processes Most flexible: ps options | other commandsps?axo?comm,tty?|?grep?ttyS0 By predefined patterns: pgrep$?pgrep?-U?root$?pgrep?-G?student By exact program name: pidof$?pidof?bash Signals Most fundamental inter-process communication Sent directly to processes, no user-interface required Programs associate actions with each signal Signals are specified by name or number when sent: Signal 15, TERM (default) - Terminate cleanly Signal 9, KILL - Terminate immediately Signal 1, HUP - Re-read configuration files man 7 signal shows complete list Sending Signals to Processes By PID: kill [signal] pid ... By Name: killall [signal] comm ... By pattern: pkill [-signal] pattern Scheduling Priority Scheduling priority determines access to the CPU Priority is affected by a process nice value Values range from -20 to 19 but default to 0 Lower nice value means higher CPU priority Viewed with ps -o comm,nice Altering Scheduling Priority Nice values may be altered...