~ubuntu-branches/ubuntu/precise/kubuntu-docs/precise-proposed

>To get a complete understanding of the Linux file system, recommended reading is the <ulink url="http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/"

>Linux Filesystem Hierarchy</ulink

> documentation hosted by <ulink url="http://tldp.org/"

>The Linux Documentation Project</ulink

>. </para>

</note>

<para

>A filesystem is a method of storing and organising files, not only in Linux but also in other computer operating systems. In Linux, most files are <quote

>regular files</quote

>, except <emphasis

>directories</emphasis

>, <emphasis

>special files</emphasis

>, <emphasis

>links</emphasis

>, <emphasis

>sockets</emphasis

>, and <emphasis

>named pipes</emphasis

>. The most common filetypes that users interact with are regular files, directories and links. </para>

<para

>Opening a terminal (in &kubuntu; this is called <application

>Konsole</application

>) and typing <screen

>ls /</screen

> brings up a list similar to the following: <screen

>bin

boot

cdrom

dev

etc

home

initrd.img

lib

lib32

lib64

lost+found

media

mnt

proc

root

sbin

selinux

srv

sys

tmp

usr

var

vmlinuz

</screen>

</para>

<note>

<para

>Not all lists will look exactly like the one above. </para>

</note>

<para

>The following is an overview of the files or directories listed above. </para>

<variablelist

><title

>Filesystem Overview</title>

<varlistentry

><term

><filename class="directory"

100

>bin</filename

101

></term>

102

103

<para

104

>Contains terminal commands that are useful to system administrators (who have full access privileges) and to regular users (who have limited access privileges). The commands in this directory are essential to the operation of a Linux system. Some of the commands in the <filename class="directory"

105

>bin</filename

106

> directory are <command

107

>bash</command

108

>, <command

109

>ls</command

110

>, <command

111

>cp</command

112

>, and <command

113

>cat</command

114

>. </para>

115

</listitem>

116

</varlistentry>

117

<varlistentry

118

><term

119

><filename class="directory"

120

>boot</filename

121

></term>

122

123

<para

124

>Contains the files required for the boot process. In the case of &kubuntu;, it contains the files for the <application

125

>GRUB2</application

126

> boot-loader, master boot records, map files, and the Linux kernel. </para>

127

</listitem>

128

</varlistentry>

129

<varlistentry

130

><term

131

><filename class="symlink"

132

>cdrom</filename

133

></term>

134

135

<para

136

>A <abbrev

137

>symlink</abbrev

138

> or <quote

139

>symbolic link</quote

140

> to <filename class="directory"

141

>/media/cdrom</filename

142

>, which itself is a <abbrev

143

>symlink</abbrev

144

> to <filename class="directory"

145

>/media/cdrom0</filename

146

>. If a <acronym

147

>CD</acronym

148

> is placed into the <acronym

149

>CDROM</acronym

150

> drive, the contents of that CD will be available in <filename class="directory"

151

>/media/cdrom0</filename

152

> directory. </para>

153

</listitem>

154

</varlistentry>

155

<varlistentry

156

><term

157

><filename class="directory"

158

>dev</filename

159

></term>

160

161

<para

162

>Location of special or device files. For example, <filename class="devicefile"

163

>/dev/sda0</filename

164

> is the first partition on the hard drive. </para>

165

</listitem>

166

</varlistentry>

167

<varlistentry

168

><term

169

><filename class="directory"

170

>etc</filename

171

></term>

172

173

<para

174

>Contains all system-related configuration files, used to control the operation of programs. </para>

175

</listitem>

176

</varlistentry>

177

<varlistentry

178

><term

179

><filename class="directory"

180

>home</filename

181

></term>

182

183

<para

184

>Contains a home directory for each user on the system. A user's home directory can contain personal configuration files and files such as documents, music, video, and other user-defined directories and files. </para>

185

</listitem>

186

</varlistentry>

187

<varlistentry

188

><term

189

><filename class="symlink"

190

>initrd.img</filename

191

></term>

192

193

<para

194

>A <abbrev

195

>symlink</abbrev

196

> to <filename

197

>/boot/initrd.img-<kernel version></filename

198

> which is required for system startup. </para>

199

</listitem>

200

</varlistentry>

201

<varlistentry

202

><term

203

><filename class="directory"

204

>lib</filename

205

></term>

206

207

<para

208

>Contains the kernel modules in addition to shared library images needed to boot the system and run commands. </para>

209

</listitem>

210

</varlistentry>

211

<varlistentry

212

><term

213

><filename class="directory"

214

>lib32</filename

215

></term>

216

217

<para

218

>Same as <filename class="directory"

219

>lib</filename

220

> above, but contains only the 32-bit versions. </para>

221

</listitem>

222

</varlistentry>

223

<varlistentry

224

><term

225

><filename class="symlink"

226

>lib64</filename

227

></term>

228

229

<para

230

>Same as <filename class="directory"

231

>lib</filename

232

> above, but contains only the 64-bit versions. </para>

233

</listitem>

234

</varlistentry>

235

<varlistentry

236

><term

237

><filename class="directory"

238

>lost+found</filename

239

></term>

240

241

<para

242

>Contains the results of any recovery operation due to an improper shutdown of the system or a system crash. </para>

243

</listitem>

244

</varlistentry>

245

<varlistentry

246

><term

247

><filename class="directory"

248

>media</filename

249

></term>

250

251

<para

252

>Contains the subdirectories which are used as mount points for removable media such as <acronym

253

>CDROM</acronym

254

> drives, <acronym

255

>USB</acronym

256

> disks, floppy disks. </para>

257

</listitem>

258

</varlistentry>

259

<varlistentry

260

><term

261

><filename class="directory"

262

>mnt</filename

263

></term>

264

265

<para

266

>Generic mount point for filesystems or devices. In most cases, <filename class="directory"

267

>/media</filename

268

> is where most devices will be automounted. </para>

269

</listitem>

270

</varlistentry>

271

<varlistentry

272

><term

273

><filename class="directory"

274

>opt</filename

275

></term>

276

277

<para

278

>Short for <quote

279

>optional</quote

280

>. This directory is used for add-on packages that are typically installed manually by the user. </para>

281

</listitem>

282

</varlistentry>

283

<varlistentry

284

><term

285

><filename class="directory"

286

>proc</filename

287

></term>

288

289

<para

290

>Virtual filesystem that contains runtime system information which is presented in a file-like structure. </para>

291

</listitem>

292

</varlistentry>

293

<varlistentry

294

><term

295

><filename class="directory"

296

>root</filename

297

></term>

298

299

<para

300

>The home directory of the system administrator known as <quote

301

>root</quote

302

>. </para>

303

</listitem>

304

</varlistentry>

305

<varlistentry

306

><term

307

><filename class="directory"

308

>sbin</filename

309

></term>

310

311

<para

312

>Contains programs that are essential to the working of the system, such as <command

313

>fdisk</command

314

>, <command

315

>ifconfig</command

316

>, <command

317

>reboot</command

318

>, and <command

319

>shutdown</command

320

>. </para>

321

</listitem>

322

</varlistentry>

323

<varlistentry

324

><term

325

><filename class="directory"

326

>selinux</filename

327

></term>

328

329

<para

330

>A pseudo-filesystem containing the commands used by the kernel subsystem for the Security-Enhanced Linux feature. </para>

331

</listitem>

332

</varlistentry>

333

<varlistentry

334

><term

335

><filename class="directory"

336

>srv</filename

337

></term>

338

339

<para

340

>Contains site-specific data which is served by the system. </para>

341

</listitem>

342

</varlistentry>

343

<varlistentry

344

><term

345

><filename class="directory"

346

>sys</filename

347

></term>

348

349

<para

350

>Contains the Linux kernel, firmware and system-related files. </para>

351

</listitem>

352

</varlistentry>

353

<varlistentry

354

><term

355

><filename class="directory"

356

>tmp</filename

357

></term>

358

359

<para

360

>Contains files that are required temporarily. Many programs use this directory to create lock files and for temporary storage of data. </para>

361

</listitem>

362

</varlistentry>

363

<varlistentry

364

><term

365

><filename class="directory"

366

>usr</filename

367

></term>

368

369

<para

370

>Contains the largest share of data on the system, including read-only user data, as well as files and programs and such as program binaries, documentation, libraries, header files, and more. </para>

371

</listitem>

372

</varlistentry>

373

<varlistentry

374

><term

375

><filename class="directory"

376

>var</filename

377

></term>

378

379

<para

380

>Contains variable data such as system log files, mail and printer spool directories, as well as transient and temporary files. </para>

381

</listitem>

382

</varlistentry>

383

<varlistentry

384

><term

385

><filename class="symlink"

386

>vmlinuz</filename

387

></term>

388

389

<para

390

>A <abbrev

391

>symlink</abbrev

392

> to a compressed executable of the Linux kernel. </para>

393

</listitem>

394

</varlistentry>

395

</variablelist>

396

</sect1>

397

398

399

400

<title

401

>Users and Groups</title>

402

<para

403

>Since Linux is a true multi-user system, the principles of both <emphasis

404

>users</emphasis

405

> and <emphasis

406

>groups</emphasis

407

> are important to the internal operation of the system, and also to the day-to-day use of the system. Linux handling of users and groups is the reason it is one of the most secure operating systems. </para>

408

409

<title

410

>Users</title>

411

<para

412

>There are two different types of users: </para>

413

414

415

<para

416

><emphasis role="strong"

417

>Physical Users</emphasis

418

> are people who use the system physically. They have user IDs which are usually unique, as well as group IDs. </para>

419

</listitem>

420

421

<para

422

><emphasis role="strong"

423

>Logical Users</emphasis

424

> are not tied to a person, but instead are tied to a system function that are used by applications to perform specific tasks. Daemons, mail, news are examples of logical users. </para>

425

</listitem>

426

</itemizedlist>

427

</sect2>

428

429

<title

430

>Groups</title>

431

<para

432

>Groups are logical expressions of organisation. They tie users together and provide group-based, rather than user-based permissions. Common groups include <emphasis

433

>admin</emphasis

434

>, <emphasis

435

>audio</emphasis

436

>, <emphasis

437

>mail</emphasis

438

>. </para>

439

</sect2>

440

</sect1>

441

442

443

444

<title

445

>Permissions</title>

446

<para

447

>In a multi-user environment, security of user and system data is important. Linux has three specific, or distinct, classes: </para>

448

449

450

<para

451

><emphasis role="strong"

452

>r</emphasis

453

> - <emphasis

454

>read</emphasis

455

> permission which grants the ability to read a file. </para>

456

</listitem>

457

458

<para

459

><emphasis role="strong"

460

>w</emphasis

461

> - <emphasis

462

>write</emphasis

463

> permission which grants the ability to modify a file. </para>

464

</listitem>

465

466

<para

467

><emphasis role="strong"

468

>x</emphasis

469

> - <emphasis

470

>execute</emphasis

471

> permission which grants the ability to execute a file. </para>

472

</listitem>

473

</itemizedlist>

474

<para

475

>The list above shows the symbolic notation of each permission in <emphasis role="strong"

476

>bold</emphasis

477

> text. Each permission also has an octal notation: </para>

478

479

480

<para

481

><emphasis role="strong"

482

>r</emphasis

483

> - <emphasis

484

>4</emphasis

485

> </para>

486

</listitem>

487

488

<para

489

><emphasis role="strong"

490

>w</emphasis

491

> - <emphasis

492

>2</emphasis

493

> </para>

494

</listitem>

495

496

<para

497

><emphasis role="strong"

498

>x</emphasis

499

> - <emphasis

500

>1</emphasis

501

> </para>

502

</listitem>

503

</itemizedlist>

504

505

<title

506

>Permissions Example</title>

507

<para

508

>To view permissions, type <screen

509

>ls -l ~/</screen

510

> which will output a list of the directories and files in the current user's home directory. For example: <screen>

511

drwxr-xr-x 2 username usergroup 4096 2009-12-17 11:10 Documents

512

</screen

513

> The first column, which contains <emphasis role="strong"

514

>drwxr-xr-x</emphasis

515

>, can be interpreted as follows: </para>

516

517

518

519

520

521

522

<thead>

523

<row>

524

<entry

525

>File Type</entry>

526

<entry

527

>User Permissions</entry>

528

<entry

529

>Group Permissions</entry>

530

<entry

531

>Others Permissions</entry>

532

</row>

533

</thead>

534

<tbody>

535

<row>

536

<entry

537

><emphasis role="strong"

538

>d</emphasis

539

> - <emphasis

540

>directory</emphasis

541

> </entry>

542

<entry

543

><emphasis role="strong"

544

>rwx</emphasis

545

> - <emphasis

546

>read</emphasis

547

>, <emphasis

548

>write</emphasis

549

> and <emphasis

550

>execute</emphasis

551

> permissions for the user. </entry>

552

<entry

553

><emphasis role="strong"

554

>r-x</emphasis

555

> - <emphasis

556

>read</emphasis

557

> and <emphasis

558

>execute</emphasis

559

> permissions for the group. </entry>

560

<entry

561

><emphasis role="strong"

562

>r-x</emphasis

563

> - <emphasis

564

>read</emphasis

565

> and <emphasis

566

>execute</emphasis

567

> permissions for all others. </entry>

568

</row>

569

</tbody>

570

</tgroup>

571

</informaltable>

572

</sect2>

573

574

<title

575

>Octal to Symbolic Summary</title>

576

577

578

<thead>

579

<row>

580

<entry

581

>Octal</entry>

582

<entry

583

>Symbolic</entry>

584

<entry

585

>Description</entry>

586

</row>

587

</thead>

588

<tbody>

589

<row>

590

<entry

591

>0</entry>

592

<entry

593

>---</entry>

594

<entry

595

>No permissions</entry>

596

</row>

597

<row>

598

<entry

599

>1</entry>

600

<entry

601

>--x</entry>

602

<entry

603

>Execute only</entry>

604

</row>

605

<row>

606

<entry

607

>2</entry>

608

<entry

609

>-w-</entry>

610

<entry

611

>Write only</entry>

612

</row>

613

<row>

614

<entry

615

>3 (2+1)</entry>

616

<entry

617

>-wx</entry>

618

<entry

619

>Write and Execute</entry>

620

</row>

621

<row>

622

<entry

623

>4</entry>

624

<entry

625

>r--</entry>

626

<entry

627

>Read only</entry>

628

</row>

629

<row>

630

<entry

631

>5 (4+1)</entry>

632

<entry

633

>r-x</entry>

634

<entry

635

>Read and Execute</entry>

636

</row>

637

<row>

638

<entry

639

>6 (4+2)</entry>

640

<entry

641

>rw-</entry>

642

<entry

643

>Read and Write</entry>

644

</row>

645

<row>

646

<entry

647

>7 (4+2+1)</entry>

648

<entry

649

>rwx</entry>

650

<entry

651

>Read, Write, and Execute</entry>

652

</row>

653

</tbody>

654

</tgroup>

655

</informaltable>

656

</sect2>

657

</sect1>

658

659

660

661

<title

662

>Processes</title>

663

<para

664

>Processes are instances of computer programs that are running. Next to files, processes are the second most important part of the Linux system. </para>

665

<variablelist

666

><title

667

>Viewing Processes in &kubuntu;</title>

668

<varlistentry

669

><term

670

>System Activity</term>

671

672

<para

673

><keycombo

674

><keycap

675

>Ctrl</keycap

676

><keycap

677

>Esc</keycap

678

></keycombo

679

> - Starts &kde;' <application

680

>s System Activity</application

681

> dialog where processes can be viewed and killed. </para>

682

</listitem>

683

</varlistentry>

684

<varlistentry

685

><term

686

>Command Line</term>

687

688

<para

689

><command

690

>ps</command

691

> - Open <application

692

>Konsole</application

693

> by going to &menukonsole; and type: <screen

694

>ps</screen>

695

</para>

696

</listitem>

697

</varlistentry>

698

</variablelist>

699

</sect1>

700

701

</article>

702

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703

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