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Lampiran B. Kursus Remedial Singkat

Meskipun buku ini terutama menarget administrator dan pengguna mahir, kita tidak ingin mengecualikan para pemula yang termotivasi. Lampiran ini karena itu adalah kursus kilat yang menggambarkan konsep-konsep fundamental yang terlibat dalam menangani komputer Unix.

B.1. Perintah-perintah Dasar dan Shell

Di dunia Unix, setiap administrator pada akhirnya mesti menggunakan baris perintah; sebagai contoh, ketika sistem gagal untuk memulai dengan benar dan hanya menyediakan mode pertolongan baris perintah. Mampu menangani antarmuka seperti itu, karenanya, adalah keterampilan dasar untuk bertahan hidup dalam keadaan ini.
This section only gives a quick peek at the commands. They all have many options not described here, so please refer to the abundant documentation in their respective manual pages.

B.1.1. Meramban Pohon Direktori dan Mengelola Berkas

Once a session is open, the pwd command (which stands for print working directory) displays the current location in the filesystem. The current directory is changed with the cd directory command (cd is for change directory). The parent directory is always called .. (two dots), whereas the current directory is also known as . (one dot). The ls command allows listing the contents of a directory. If no parameters are given, it operates on the current directory.
$ pwd
/home/rhertzog
$ cd Desktop
$ pwd
/home/rhertzog/Desktop
$ cd .
$ pwd
/home/rhertzog/Desktop
$ cd ..
$ pwd
/home/rhertzog
$ ls
Desktop    Downloads  Pictures  Templates
Documents  Music      Public    Videos
A new directory can be created with mkdir directory, and an existing (empty) directory can be removed with rmdir directory. The mv command allows moving and/or renaming files and directories; removing a file is achieved with rm file.
$ mkdir test
$ ls
Desktop    Downloads  Pictures  Templates  Videos
Documents  Music      Public    test
$ mv test new
$ ls
Desktop    Downloads  new       Public     Videos
Documents  Music      Pictures  Templates
$ rmdir new
$ ls
Desktop    Downloads  Pictures  Templates  Videos
Documents  Music      Public

B.1.2. Menampilkan dan Mengubah Berkas Teks

The cat file command (intended to concatenate files to the standard output device) reads a file and displays its contents on the terminal. If the file is too big to fit on a screen, use a pager such as less (or more) to display it page by page.
The editor command starts a text editor (such as vi or nano) and allows creating, modifying and reading text files. The simplest files can sometimes be created directly from the command interpreter thanks to redirection: echo "text" >file creates a file named file with “text” as its contents. Adding a line at the end of this file is possible too, with a command such as echo "moretext" >>file. Note the >> in this example.

B.1.3. Mencari Berkas dan di dalam Berkas

The find directory criteria command looks for files in the hierarchy under directory according to several criteria. The most commonly used criterion is -name name: that allows looking for a file by its name.
The grep expression files command searches the contents of the files and extracts the lines matching the regular expression (see sidebar BACK TO BASICS Regular expression). Adding the -r option enables a recursive search on all files contained in the directory passed as a parameter. This allows looking for a file when only a part of the contents are known.

B.1.4. Mengelola Proses

The ps aux command lists the processes currently running and helps identifying them by showing their pid (process id). Once the pid of a process is known, the kill -signal pid command allows sending it a signal (if the process belongs to the current user). Several signals exist; most commonly used are TERM (a request to terminate gracefully) and KILL (a forced kill).
The command interpreter can also run programs in the background if the command is followed by a “&”. By using the ampersand, the user resumes control of the shell immediately even though the command is still running (hidden from the user; as a background process). The jobs command lists the processes running in the background; running fg %job-number (for foreground) restores a job to the foreground. When a command is running in the foreground (either because it was started normally, or brought back to the foreground with fg), the Control+Z key combination pauses the process and resumes control of the command-line. The process can then be restarted in the background with bg %job-number (for background).

B.1.5. Informasi Sistem: Memori, Ruang Disk, Identitas

The free command displays information on memory; df (disk free) reports on the available disk space on each of the disks mounted in the filesystem. Its -h option (for human readable) converts the sizes into a more legible unit (usually mebibytes or gibibytes). In a similar fashion, the free command supports the -m and -g options, and displays its data either in mebibytes or in gibibytes, respectively.
$ free
             total       used       free     shared    buffers     cached
Mem:       1028420    1009624      18796          0      47404     391804
-/+ buffers/cache:     570416     458004
Swap:      2771172     404588    2366584
$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2              9614084   4737916   4387796  52% /
tmpfs                   514208         0    514208   0% /lib/init/rw
udev                     10240       100     10140   1% /dev
tmpfs                   514208    269136    245072  53% /dev/shm
/dev/sda5             44552904  36315896   7784380  83% /home
The id command displays the identity of the user running the session, along with the list of groups they belong to. Since access to some files or devices may be limited to group members, checking available group membership may be useful.
$ id
uid=1000(rhertzog) gid=1000(rhertzog) groups=1000(rhertzog),24(cdrom),25(floppy),27(sudo),29(audio),30(dip),44(video),46(plugdev),108(netdev),109(bluetooth),115(scanner)