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本文介绍了Linux环境下几个常用命令的使用方法，包括如何使用nohup后台运行进程、cut命令提取文件特定列或字符、tar命令进行文件归档及恢复、cpiocommand命令复制文件到磁带或从磁带恢复文件等。此外还介绍了如何使用sar命令监控系统资源使用情况，以及crontab设置定时任务的方法。

Here's how you specify the nohup option for a process:

$ nohup test.ksh

$ test.ksh &
[1]    27149

================================
Outputting Columns with the cut Command
The cut command will output specified columns from a text file. Let's say you have a file named example.txt with the following text:
one two three
four five six
seven eight nine
ten eleven twelve
You can specify the fields you want to extract with the -f option. The following command will return just the second column in the example.txt file:
$ cut -f2 example.txt
two
five
eight
eleven
 You use the -c option with the cut command to specify the specific characters you want to extract from a file. The following two commands extract the tenth character and then characters 10-12 from the password.txt file:
$ password.txt | cut -c10
$ password.txt | cut -c10-12

=====================================
$ test "ONE" = "one"
$ echo $?
0
========================================
The following tar command will copy the data01.dbf file to a tape, with the format /dev/rmt/0m. The -cvf option creates a new archive (the hyphen is optional). The c option asks tar to create a new archive file, and the v option stands for verbose, which specifies that the files be listed as they are being archived: $ tar -cvf /dev/rmt/0m   /u10/oradata/data/data01.dbf
The following tar command will extract the backed-up files from the tape to the specified directory:
$ tar -xvf/dev/rmt/0m    /u20/oradata/data/data01.dbf

 The x option asks tar to extract the contents of the specified file. The v and f options have the same meanings as in the previous example.
The cpio command with the -o (copy out) option copies files to standard output, such as disk or tape. The following command will copy the contents of the entire current directory (all the files) to the /dev/rmt/0m tape:
 $ ls | cpio -0 > /dev/rmt/0m
 
 The cpio command with the -i (copy in) option extracts files from standard input. The following command restores all the contents of the specified tape to the current directory:
$ cpio -i < /dev/rmt/0m
========================================
$ crontab -e
 Each line in the crontab is an entry for a regularly scheduled job or program, and you edit the crontab the same way you edit any normal vi-based file. Each line in the /etc/crontab file represents a job that you want to execute, and it has the following format:
minute         hour     day    month     day of week       command
=======================================
$ sar -u 1 10
HP-UX prod5 B.11.11 U 9000/800   04/07/08

16:11:21    %usr      %sys      %wio   %idle
16:11:22      34         6        56       4
16:11:23      31         7        55       7
16:11:24      45         9        43       4
16:11:25      45         9        44       2
16:11:26      45        11        40       3
16:11:27      46        11        40       4
16:11:28      48        10        40       3
16:11:29      56        11        31       2
16:11:30      50        12        36       3
16:11:31      45        12        39       4

Average       44        10        42       4
$
=======================================================