Symbols<, 28<<, 265>, 27–28>>, 27–28[, 256–261$, xxi, 12–13, 22, 290$#, 254$$, 255$0, 255$1, 254$?, 255–256. See also exit code$@, 254–255#, xxi, 13. See also root#!, 249–250, 325|, 19, 27, 39/, 40, 93, 95–97, 99–100*, 17–18, 21, 251–252. See also regular

expressions

Aabstraction, 1–2administrator. See rootalias, 290–291ALSA, 53Apache, 346Apple partition, 73application layer, 191, 229–232archive, 37–39

table of contents, 38testing, 38, 330–331

ARP, 225–226at, 161ATA, 62autoconf, 332–336autotools, GNU, 330, 342. See also

autoconfAvahi, 208, 239awk, 266

Bbasename, 265–266bash, 12. See also Bourne Shell

startup file, 292–295bg, 32/bin, 40/bin/bash. See bash/bin/sh. See Bourne ShellBIOS, 97

boot partition, 108bison, 325blkid, 76block bitmap, 90blockdev, 70block device, 46–48, 53, 61, 63,

65–67, 70/boot, 41, 102–103boot, 93–94. See also init

loader, 93, 97–98chainloading, 106–107filesystem access, 97, 101–102GRUB, 102internals, 107–109multi-stage, 107for systems other than Linux,

106–107messages, 94–95network configuration, 202–203

Bourne Shell, 12basic use, 12–13Bourne-again, 12script (see shell script)

building software, 330–333, 340–342bunzip2, 39bus error, 30BusyBox, 349bzip2, 39

Index

356 Index

CC, 310–311

compiler, 320–321, 340–341preprocessor, 312–313, 321, 335,

341–342case, 262cat, 13cd, 16–17chainloading, 106–107character device, 46–47, 53child process, 175Chrome OS, 308chsh, 12, 21, 166–168chvt, 52, 300CIDR, 195clang, 310CLASSPATH, 327clobber, 27cloud computing, 348CMake, 331, 342command-line editing, 24command substitution, 263–264compiling, 310–311compositing window manager, 305compressing files, 37–39, 277concatenating files, 13configuration file, 40, 149–150configure, 332–336context switch, 5–6control group, 123controlling terminal, 51coreboot, 98coreutils, 332–333, 338cp, 15cpio, 146cpp, 312–313, 321, 335, 341–342CPU, 2–4

multiple, 6, 176time, 171–172, 178–181, 183–185

CPU time, 32cron, 159–161csh, 294

ctrl-C, 14

ctrl-D, 13–14CUPS, 307–308curl, 230–232current working directory, 16, 19–20,

172–173cylinder, 71–72

Ddaemon, 149database, 346–347date, 157–158D-Bus (Desktop Bus), 58, 124–125,

203, 299, 305–307instance, 306monitoring, 306–307

dd, 48–49, 83debugfs, 84debugger, 323–324default gateway, 196, 201demand paging, 182desktop, 297–298

background, 304environment, 299

Desktop Bus. See D–Bus/dev, 40, 46–48device, 45

audio, 53block, 46–48, 53, 61, 63, 65–67, 70character, 46–47, 53copy, 48–49creating file, 53–54disk, 46–48driver, 4, 7, 93file, 40, 46–47, 53–57, 80finding, 48–49information, 47–48, 57–58initialization, 53–58major and minor numbers, 47–49monitor, 57–58name, 47–53network, 47node, 40, 46–47, 53–57, 80optical, 51, 63–64, 73parallel, 52pipe, 47, 53SCSI (see SCSI)serial, 52socket, 47, 247–248terminal, 51–52types, 46–47

/dev/hd*, 51/dev/lp*, 52/dev/null, 46/dev/parport*, 52/dev/pts, 51/dev/sd*, 50–51

Index 357

/dev/sg*, 51, 63–64/dev/snd, 53/dev/sr*, 51, 63–64devtmpfs, 53–55/dev/tty*, 51–52/dev/zero, 48–49df, 81DHCP, 214–215diff, 20, 256, 339directory, 16, 33

change, 16–17create, 17current, 16, 19–20, 172–173errors, 30hierarchy, 16, 40–42home, 17, 40, 154–155internal structure, 88listing contents, 14–15parent, 16, 88–90permissions, 35remove, 17root, 40, 93, 95–97, 99–100

diskaddressing, 71–72buffer, 77cache, 77capacity, 69copy, 48–49device, 50–51, 65–68device file, 46–48format, 68, 74–75geometry, 70–72monitoring usage, 183–187partition (see partition)PATA, 51quota, 188raw access, 48–49, 67SATA, 50–51, 56, 62scheduling priority, 187schematic, 65–66SCSI, 50–51, 59–62solid-state, 72, 91swap 80, 85–86usage, 81

display, 300manager, 300modes, 51–52

dmesg, 49, 94–95, 153. See also kernel: log

DNS (Domain Name Service), 198–199, 206–209

documentation, 25–27Domain Name Service (DNS),

198–199, 206–209dot file, 21, 287DPMS, 305du, 81

Ee2fsck. 80, 82–84echo, 13, 16EDITOR, 295–296effective user ID (euid), 162–165EFI, 97–98, 105–108

ESP, 108–109secure boot, 106

efilinux, 98egrep, 18elapsed time, 178–179Emacs, 24–25embedded system, 348–349encryption, 170, 233–234environment variable, 21–22,

268–269error message, 27–30, 175ESP, 108–109. See also EFI/etc, 40, 149–150/etc/fstab, 50, 77, 79–81/etc/hosts, 207/etc/init.d, 142/etc/inittab, 139–141/etc/ld.so.cache, 316/etc/ld.so.conf, 316/etc/localtime, 158/etc/login.defs, 170/etc/mtab, 78/etc/nologin, 144/etc/nsswitch.conf, 207–209, 346/etc/passwd, 26, 153–155, 164–165, 346/etc/profile, 292/etc/rc.d, 140–142/etc/resolv.conf, 207/etc/services, 211/etc/shadow, 154–155/etc/shells, 155, 166–168Ethernet, 199–200, 225–226

wireless, 226–228euid (effective user ID), 162–165

358 Index

exec(), 7, 174, 268executable, 34–35, 40–41, 78,

310–311, 325exit code, 255–257export, 22

Ffdisk, 68–70fg, 32–33files, 20

comparing with another file, 20compressing, 37–39, 277copying, 15creating empty, 15deleting, 16, 89descriptor, 172–173details, 14–15device, 40, 46–47, 53–57, 80dot, 21, 287errors, 29–30find, 20find text in, 18–19format, 20group, 14–15, 33–34identify, 259–260link, 36, 87–90, 260link count, 89–90listing, 14–15mode, 33–35move, 15open, 172–174owner, 14–15, 33–34permissions (see permissions)redirecting

command input from, 28command output to, 27–28

regular, 33rename, 15sharing

across a network, 278–286with other users, 9–10

socket, 47, 247–248swap, 85temporary, 264–265test, 259–260transfering, 271

with Python, 271rsync, 272SSH, 236–237

type, 33, 35, 46, 173updating timestamp, 15

filesystem, 66–67, 72–73Btrfs, 74, 91capacity, 81check, 82–84CIFS, 285creating, 68, 74–75currently attached, 75–76ext2/ext3/ext4, 73–77, 82–84FAT, 73HFS+, 73hierarchy, 40–42internal structure, 74, 87–90ISO 9660, 73, 78journal, 73, 82–83mount, 75–80, 114, 130–131

options, 77–80NFS, 285–286proc, 40, 79–80, 84read-only, 78–79, 96remount, 79repair, 82–84tmpfs, 84type, 73–74usage, 81user space, 73

interface, 90–91UUID, 50, 76–77, 79, 96, 99–101

find, 20, 267–268finding command, 25firewall, 219–221

rule, 221–223strategy, 223–224

flex, 325for, 262fork(), 7, 123–124, 136–137, 174, 176,

232–233frame, 199free, 85fsck, 80, 82–84FTP, 237, 245

Ggateway, 192, 196gcc, 310gdb, 323–324gdisk, 68GECOS, 154

Index 359

geteuid(), 164–165getty, 52, 120, 135–136, 140, 157Ghostscript, 308glob, 17–18, 21, 251–252. See also

regular expressionGNU autotools, 330, 342. See also

autoconfgparted, 67–69GPT, 67–69, 101grep, 18–19, 256–257group, 10, 154, 156–157

listing, 34permissions, 33–35

groups, 34GRUB, 98

boot command, 102command line, 100–101configuration, 98–99, 102–104devices, 100–101filesystem access, 101–102insmod, 99–100install, 104–106internals, 108–109menu, 98–99, 103on removable media, 105–106root, 99–102

grub-mkconfig, 103–104GTK+, 299guest operating system, 347–348gunzip, 37–39gzip, 37–39

Hhalt, 144–145hard link, 36, 87–90, 260hardware operation, 4head, 21, 71–72header file, 41, 311–312, 335, 337

locating, 341–342help, 25–27here document, 265/home, 40home directory, 17, 40, 154–155host, 190, 198–199host key, 234–236HTTP, 230–232hypervisor, 348

IICMP, 197–198ifconfig, 193–194, 200–202if/then/else, 256–258image, 4include file, 311–313, 335, 336inetd, 237info, 26–27, 43init, 93–95, 112–113. See also systemd;

Upstartidentifying, 114process tracking, 112–113runlevel, 113

systemd, 129System V, 139–142Upstart, 138–139

sequence, 112, 141–143System V, 112–114, 129, 138–143

initctl, 132initramfs, 99–100, 109, 145–146initrd, 146. See also initramfsinode, 82, 87–90, 260

root, 88–90installing software, 329–330, 338interactive shell, 292–294Internet layer, network, 191–192. See

also IPiostat, 185–186iotop, 186–187IP, 192

address, 192–194, 200–202, 216–217

chain, 220–224filter, 219–220forwarding, 216subnet, 192–195

choosing, 216–217mask, 194–195, 201routing between, 215–216table, 220

IPP, 307–308iptables, 221–224IPv4, 192IPv6, 192

JJava, 327–328job control, 32jobs, 32

360 Index

Kkernel, 2–5

as a resource, 171boot, 93, 95–96boot messages, 94–95compiling, 343disk buffer, 77disk cache, 77disk I/O system, 66–67, 86load, 93, 97–98location, 42log, 58–59, 153modules, 42network interface, 47, 200–203parameters, 96–97, 99–100reading partition table, 69–70ring buffer, 94routing table, 196SCSI subsystem, 58–64

kernel mode, 3kernel space, 3keyboard, 302–304kill, 31–32

LLAN, 190layer, 2

network, 189–192LBA, 71–72, 97LDAP, 346ldconfig, 316ldd, 315–316LD_LIBRARY_PATH, 296, 316–317ld.so, 315–316less, 19, 293–294, 296, 336level, 2

in user space, 8–9Lex, 324–325/lib, 40libata, 60, 62library, 40, 336–337

linking against, 313–314, 316–317, 321

shared, 40, 314–317, 334–335, 337system calls, 174–175trace, 176

LILO, 98

linkcount, 89–90farm, 142hard, 36, 87–90, 260symbolic, 35–36

listen, 210–211, 239–240literal, 251–253LLVM, 310, 328ln, 35–36, 87, 89–90loadable kernel modules, 42load average, 180–181LOADLIN, 98localhost, 205, 209locate, 20log, 9. See also kernel, log; syslog

kernel, 58–59, 153syslog, 150–153system, 121Upstart, 134, 138

logger, 153login, 157login shell, 292–294logrotate, 153loops, 262–263lost+found, 83, 90ls, 14–15lsof, 172–174

network, 239Unix domain socket, 248

lsscsi, 50, 59, 63lsusb, 62ltrace, 176

MMAC address, 199–200, 205–206,

225–226main memory. See memorymake, 318–323Makefile

dependency, 318–319, 323organization, 322–323rule, 318–319separator, 319–320staying up-to-date, 320target, 318–319

standard 322, 336man, 25–26. See also manual pagemanual page, 25–27, 42, 290

Index 361

MBR, 67–69, 101boot, 107–108

mDNS, 208/media, 41memory, 3–4

capacity, 85–86, 181insufficient, 84, 86, 181management, 6, 95, 182–183monitoring usage, 183–185page, 182protection, 3swap, 80, 85–86

partitions, 68–69, 85test, 104virtual, 6, 85

Mir, 305mkdir, 17mkfs, 74–75mknod, 53–54mkswap, 85MMU, 6, 182modules, kernel, 42mount, 75–80. See also filesystem:

mountmouse, 303–304multitasking, 5–6mv, 15

NNAT, 216–218netcat, 241–242netstat, 210–211, 238network, 189–191

application layer, 191, 229–232client, 210configuration, 193–194,

200–203, 214 connection, 210–211, 230,

239–241firewall, 219–221

rule, 221–223strategy, 223–224

host, 190, 198–199interface, 47, 200–203Internet layer, 191–192layer, 189–192localhost, 205, 209packet, 190–191

physical layer, 191port, 210–211, 230prefix, 194private, 216–217promiscuous mode, 240route, 195–196, 198router, 190, 192–193, 196–197,

215–216, 218–21server, 210, 232–233simple, 190, 192–193, 214stack, 191transport layer, 191–192troubleshooting, 197–198,

239–242wireless, 202–204

network configuration manager, 203–206

NetworkManager, 203–206, 228Network Time Protocol (NTP),

158–159, 212NFS, 285–286nftables, 220nice value, 179–180nmap, 242–243NTP (Network Time Protocol),

158–159, 212

Oobject file, 311OOM killer, 86open(), 175open source, 329OpenWRT, 219, 349/opt, 41OSS, 53

Ppackage, 333–334, 338, 341–343packet, 190–191page, 182

fault, 182–183table, 6, 182

PAGER, 296pager, 19, 296PAM (Pluggable Authentication

Modules), 165–170parallel port, 52parted, 67–70

362 Index

partition, 50alignment, 72altering table, 67–70Apple, 73capacity, 69, 81extended, 68–69geometry, 70–72logical, 68–69primary, 68reading table, 69–70swap, 68–69, 85system ID, 69table, 66–70viewing, 68–69Windows, 73

passwd, 21, 34, 155–156password

changing, 21, 170file, 26, 153–155, 164–165, 346

patch, 339patchelf, 317path, 16PATH, 22–23, 288–290path

absolute, 16command, 22–23, 288–290relative, 16

pathname. See pathperformance, 171

memory, 86Perl, 19, 326permissions, 30, 33–35

bits, 34changing, 34–35default, 35, 291directory, 35execute, 34–35group, 33–35other, 33–35preserving, 38read, 33–35testing, 260user, 33–35world, 33–35write, 33–35

physical layer, 191, 199–200Pico, 25PID (process ID), 30–32, 177, 255pidstat, 187–188ping, 197–198

pipe, 19, 27, 39named, 47, 53

pkg-config, 336–338Pluggable Authentication Modules

(PAM), 165–170plymouth, 51–52port scan, 242–243printing, 52, 307–308private network, 216–217/proc, 40, 79–80, 84process, 2–4, 30–33, 84

accounting, 188background, 32–33blocked, 185child, 175continue, 32ID, 30–32, 177, 255interface, 40list, 30–31management, 5memory, 6, 86, 172monitoring, 187–188open files, 172–174owner, 9, 162–163priority, 179–180starting new, 7status, 31stop, 31–32terminate, 31–32tracking, 172unexpected termination, 86

.profile, 292prompt (shell), 12–13, 22, 290ps, 30–31, 162–163, 183pseudodevice, 8pseudoterminal, 51pulseaudio, 53pwd, 19–20Python, 325–326

QQt, 299

RRaspberry Pi, 349real-time clock, 157real user ID (ruid), 162–163reboot, 144–145redraw display, 33

Index 363

regular expressions, 19regular file, 33relational database, 347remote login, 233–237renice, 180replication, 347resource monitoring, 178reverse isearch, 33RIP, 308rm, 16rmdir, 17root, 9–10

directory, 40, 93, 95–97, 99–100prompt, 13running programs as, 42–43

route, 195, 201–202route (network), 195–196, 198

configuration, 200–201router, 190, 192–193, 196–197,

215–216, 218–219RPC, 243rsync, 271

bandwidth, 277compression, 277copying

from remote host, 277to remote host, 271–274

exact copy, 273–274excluding files, 275–276verifying transfer, 276–277

rsyslogd, 151–153ruid (real user ID), 162–163runlevel, 113

System V, 139–142systemd, 129Upstart, 138–139

run-parts, 143runtime

information, 41library search path, 316

SSamba, 278–285

client, 283–285sar, 188SATA, 59–60saved user ID, 163/sbin, 41scheduling tasks, 159–161

SCons, 342scp, 237screen, 32scripting language, 325–327SCSI, 50, 58–64

disk, 50–51, 59–62generic, 51, 63–64ID, 58–59listing device information, 50,

59, 63sector, 71–72security, 162–170

in command path, 289network, 243–245

sed, 266–267segmentation fault, 30serial port, 52

USB, 52server role, 8–9setuid, 34, 78, 162–163sftp, 237shadow password, 154–155shared library, 40, 314–317,

334–335, 337system calls, 174–175trace, 176

shebang, 249–250, 325shell, 12. See also Bourne Shell

change, 12, 21editing commands, 24prompt, 12–13, 22, 290quoting, 251–253user, 154–155variables, 21–22, 31, 253

special variables, 253–255window, 12, 32–33, 51

shell script, 12, 249–250arguments, 254–255arithmetic, 261, 268, 270conditional, 256–257include, 269limitations, 250, 270loops, 262–263name, 255permission, 250PID, 255reading user input, 269string test, 260–262

shortcut. See symbolic linkshutdown, 144–145

364 Index

signal, 31–32, 264–265single-user mode, 96, 113, 146–147socket, 246–247

device, 47, 247–248Unix domain, 247–248

solid-state disk (SSD), 72, 91sort, 21sound, 53source code, 310special characters, 23–24splash screen, 51–52, 94, 96SQL, 347SSD (solid-state disk), 72, 91SSH, 119, 136–137, 233–237standard error, 27–28, 33, 160standard I/O, 13–14

input, 14, 19, 28, 33, 37, 49output, 14, 19, 27–28, 33, 37,

49, 160redirection, 27–28

startup. See bootstartup file, 287–290

example, 293–295order, 291–295

stat, 89–90stat(), 90state, 4static library, 314stderr, 27–28, 33, 160stdin, 14, 19, 28, 33, 37, 49stdio, 13–14, 310–311

redirection, 27–28stdout, 14, 19, 27–28, 33, 37, 49, 160strace, 137, 174–175stream, 19, 27–28, 46–49

edit, 266–267ID (in shell), 28I/O, 13–14search, 18–19, 256–257

su, 42–43subnet, 192–195

choosing, 216–217mask, 194–195, 201routing between, 215–216

subshell, 268–269sudo, 43, 163superblock, 74, 83, 90superserver, 237superuser. See root

swap, 80, 85–86partitions, 68–69, 85

swapoff, 85swapon, 85symbolic link, 35–36sync, 77/sys. See sysfssyscall. See system callsysfs, 45, 47–48, 55, 84SYSLINUX, 98syslog, 150–153system call, 4, 7–8

trace, 174–175system clock, 157–159systemctl, 116, 118, 120–121systemd, 112–114

activating unit, 120, 123, 128configuration, 117–120creating unit, 122–123deactivating unit, 123dependency, 114–117disabling unit, 123enabling unit, 119–120, 123job, 121–122log, 121mount unit, 81, 114, 118on-demand resource, 124–129operating, 120–122parallel unit activation, 125–127process tracking, 123–124service unit, 114, 119, 127–129socket unit, 127–128, 237specifier, 120startup, 114System V compatibility, 129target unit, 114unit, 114–115

file, 118–120instance, 128

variable, 120system messaging, 151system time, 178–179System V init, 112–114, 129, 138–143

Ttail, 21tar, 37–39, 269

Index 365

TCP, 209–213, 218filtering, 222–224interacting with service, 230–232

tcpdump, 240–241TCP wrapper, 238tcsh, 292–295telnet, 230, 233, 241, 245tempfs, 84temporary file, 264–265terminal, 51–52. See also shell: window

controlling, 51device, 51–52virtual, 51–52, 113, 135–136, 300

test, 256–261text editor, 24–25, 295–296text search, 18–19thrash, 181. See also memory:

insufficientthread, 176–178time, 178–179. See also CPU time;

elapsed time; system timetime (of day), 157–159time slice, 5/tmp, 41toolkit, 299top, 172, 178–179touch, 15traceroute, 198transport layer, 209. See also network,

application layertroubleshooting, 151–153tune2fs, 77

Uudev, 45, 48–50, 53–58

configuration and rules, 55–56event, 55, 58

udevadm, 48–50, 57–58, 70udevd, 53–58, 77udisks-daemon, 58UDP, 209, 212, 218, 240UEFI, 97–98, 105–108

ESP, 108–109secure boot, 106

uevent, 55, 58umask, 35, 291umount, 76–77

Unix, 11Unix domain socket, 247–248unlinking, 89. See also files: deletingunxz, 39unzip, 39Upstart, 112–113, 130

configuration, 133–135event, 112, 130–131, 133–135, 137job, 130–133, 137–138log, 134, 138mounting filesystems, 130–131,

133–134operation, 137–138process tracking, 136–137runlevel, 138–139startup, 130–131System V compatibility, 138–139

uptime, 180USB, 61–62

listing device information, 62relationship to SCSI, 50, 60–62serial port, 52

user, 9–10authentication, 164–170authorization, 164changing, 42–43environment, 287–288ID, 9, 153–155, 162–164identification, 164–165management, 154–157mode, 3process (see process)regular, 12root (see root)

user space, 2–3filesystem, 73

interface, 90–91organization, 8–9start, 93, 95–96, 111–112

userland. See user spaceusername, 9, 153–155/usr, 41–42/usr/lib, 314/usr/local, 41, 334, 338/usr/share, 41UTC, 157–158UUID, 50, 76–77, 79, 96, 99–101

366 Index

V/var, 41/var/log, 151–153VFS, 73, 90vi, 24–25vipw, 155–156virtual console, 51–52, 113,

135–136, 300virtual machine, 327, 347–348virtual memory, 6, 85. See also

memory: managementvmstat, 183–185

Wwallpaper. See desktop backgroundwarning messages, 29Wayland, 305web application, 346web server, 271, 346WEP, 228while, 262–263who -r, 113widget, 299wildcard. See globwindow manager, 298–299Windows

boot, 106–107file sharing, 278–285partition, 73password, 280–281printer sharing, 283

wireless network, 202–204. See also Ethernet: wireless

worker process, 232–233WPA, 228

Xxargs, 267–268xev, 302X event, 301–302xinetd, 237xinput, 303–304XKB, 304xlsclients, 301xmodmap, 302, 304xset, 305X Window System

application, 299client, 298, 301diagnostics, 301–305display (see display)event, 301–302future, 305input, 302–304network transparency, 300–301preferences, 302–305server, 51, 298–300tunneling, 233–234, 301window manager, 298–299

xwininfo, 301xz, 39

YYacc, 324–325

Zzcat, 39zip, 39

How Linux Works, 2nd Edition is set in New Baskerville, TheSansMono Condensed, Futura, and Dogma. The book was printed and bound by Edwards Brothers Malloy in Ann Arbor, Michigan. The paper is 60# Husky Opaque, which is certified by the Sustainable Forestry Initiative (SFI).

The book uses a RepKover binding, in which the pages are bound together with a cold-set, flexible glue and the first and last pages of the resulting book block are attached to the cover with tape. The cover is not actually glued to the book’s spine, and when open, the book lies flat and the spine doesn’t crack.