Index

A

  • a escape sequence, 174
  • aa-complain command, 115
  • aa-disable command, 119
  • aa-unconfined command, 113
  • AAA (Authentication, Authorization, Accounting) services, 116
  • --abort option for merge conflicts, 176
  • access control lists
    • files, 111
    • policies, 149
    • Squid, 73–74
  • accounts
  • acl command, 73
  • active-backup mode for network bonding, 30
  • active/passive mode for network bonding, 30
  • addresses. See IP addresses
  • age limits for passwords, 121
  • agent orchestration, 164, 198
  • agentless orchestration, 183
  • alerts, escape sequences for, 174
  • aliased commands, 178
  • aliases for email, 66
  • allow-guest=false option, 135
  • AllowUsers directive, 108
  • alsamixer command, 82
  • anaconda and kickstart, 31
  • Ansible package, 162
  • Apache servers
    • configuration file, 77
    • restarting, 75
    • SSL private keys, 83
  • AppArmor
  • appending output
    • to files, 167
    • to STDOUT, 78
  • apt-cache search command, 51, 188
  • apt-get update command, 52, 130
  • apt-get upgrade command, 48, 129
  • archive mode for rsync command, 71
  • arguments, number of, 177
  • arp command, 144–145
  • arrays
  • at now command, 62
  • atq command, 189
  • atrm command, 63
  • attributes for files, 154, 156
  • audio, mixer volumes, 82
  • auditd daemon, 117
  • ausearch command, 152
  • authentication
  • Authentication, Authorization, Accounting (AAA) services, 116
  • authoritative name servers, querying, 16
  • authorization
  • authorized_keys file, 98
  • autofs automounter, 70
  • automatic logouts, 177
  • automation
    • build, 168, 180
    • configuration management, 166
    • infrastructure, 165, 178
    • inventory attributes, 174
  • automount options, 70
  • AVC messages, 155
  • awk command, 195

B

  • background tasks, viewing, 133
  • backquotes (`) for commands, 168
  • backslashes () for escape characters, 163
  • backups
    • extracting files from, 117
    • incremental, 114
    • patch command, 198
  • backward searches with less command, 58
  • bad blocks
    • checking for, 147
    • displaying, 23
  • balance-rr mode for bonding scenarios, 35
  • bare-metal hypervisors, 34
  • baseurl option for package repositories, 72
  • .bash_history file, 195
  • .bash_profile file, 60
  • Bash shell, invoking, 163
  • bcfg command, 22
  • bell, escape sequences for, 174
  • /bin/false shell, 135
  • BIND
    • chroot scenario, 103
    • reloading, 77
    • server configuration, 73
    • server control, 79
  • biometric authentication, 114
  • BIOS
    • passwords, 114
    • SATA disks, 194
  • blacklist information for modules, 21
  • blkid command
  • blob storage, 31
  • block devices, information on, 142
  • blocks
  • Bluetooth devices, detecting, 85
  • bonded-link aggregation, 33
  • bonding scenarios, load balancing in, 35
  • /boot/efi partition, 5
  • /boot/grub/grub.conf file, 110
  • /boot partition
    • mounting in, 22
    • size, 7
  • boot times for services, 76
  • booting
    • changing order, 22
    • configuration, 22
    • device checking order, 12
    • from HTTP and FTP, 28
    • kernel ring buffer, 5
    • kickstart, 35
    • location, 27
    • lsblk command, 72
    • preventing, 114
    • single-user mode, 5
    • troubleshooting, 129
  • bootloaders
  • brace expansion in echo command, 164
  • brctl command, 36
  • bridging vs. NAT, 30
  • btrfs filesystems, 11
  • buffers column for memory usage, 150
  • build automation, 168, 180
  • build files, excluding, 176
  • bypassing
    • locale translations, 14, 179
    • routing tables, 198
  • byte-to-inode ratio, 149
  • bzImage, creating, 191
  • bzip2 command, 103

C

  • caches
    • Kerberos authentication, 112
    • package, 52
    • purging, 33
    • shared libraries, 48, 129
  • Cacti tool, 143
  • caja file manager, 76
  • carriage returns, escape characters for, 198
  • case statements
    • clause ends, 178
    • default case, 169
    • terminating, 173
  • cat /etc/passwd command
    • contents output, 55
    • description, 179
    • usernames, 54
  • cat /proc/interrupts command, 46, 186
  • CentOS 7 bug-reporting tool, 78
  • certificate authority servers, 73
  • Certificate Signing Requests (CSRs), 77
  • certificates in Postfix TLS, 105
  • cfq scheduler, 150
  • chage command
  • chaining commands, 169, 174
  • change date for passwords, 64, 69
  • character case, converting, 83
  • characters
    • attributes, 189
    • multibyte representation, 13
    • supported character sets, 32
  • chattr command, 154
  • chcon command, 113
  • checksums for files, 118
  • chgrp command
    • group ownership, 94–95
    • web servers, 59
  • chkconfig —level command, 79
  • chkconfig —list command, 47
  • chmod command
    • permissions, 111
    • privileges, 95
    • recursive changes, 95, 169
    • script execution, 162
    • sticky bits, 95
  • chown command, 118, 152
  • chroot scenario with BIND, 103
  • CIFS (Common Internet File System), 32
  • clock
    • setting, 15
    • UTC time, 15
    • working with, 14
  • cloning repositories, 165, 177, 195
  • cloud-init command, 32
  • cluster servers, 79
  • collection of devices, 163
  • command execution
    • customized environments, 162
    • on logout, 171
    • in non-interactive sessions, 99
    • source commands, 171
    • subshells, 166
  • command-line interface for Network Manager, 150
  • commands
  • comments
    • /etc/inetd.conf file, 100
    • scripts, 164
  • commits
  • automatic, 180
  • history, 168, 174
  • Common Internet File System (CIFS), 32
  • comparing
  • complain mode for AppArmor profiles, 115
  • completed print jobs in CUPS, 67
  • compression
    • .gz files, 72
    • logs, 97
    • lzma files, 94
    • tar command, 102
  • configuration management automation, 166
  • connection points for USB disks, 129
  • connections
    • hypervisors, 32
    • SSH, 197
    • troubleshooting, 140
    • USB devices, 48
    • X severs, 135
  • console logins by root user, 111
  • containers, 75
  • contexts
  • converting character case, 83
  • copying
  • cp command
    • directories, 55
    • overwriting files, 55
  • cpio utility, 117
  • cron
    • directory, 63
    • entry lists, 65
    • job execution, 62
    • scheduled tasks, 96
    • system-wide files, 63
    • users, 62
  • crontab command
    • entry lists, 65
    • removing jobs, 196
  • cryptsetup command, 101
  • CSRs (Certificate Signing Requests), 77
  • Ctrl+Alt+Del keys, disabling, 110
  • Ctrl+C keys
  • terminating daemons, 77
  • terminating scripts, 175
  • Ctrl+Z keys for suspending daemons, 83
  • CUPS system
    • completed print jobs, 67
    • configuration, 66
    • default ports, 67, 152
    • restarting, 68
  • curl command, 80
  • currency-related localization, 14, 181
  • current default route, 199
  • currently mounted filesystems, 10
  • custom commands for kernel modules, 30
  • custom logs, 67
  • customized environments, command execution in, 162
  • cut command, 55
  • CVE process for security bulletins, 116

D

  • daemons
    • configuration files, 81
    • local servers, 149
    • stopping, 81
    • suspending, 83
    • terminating, 77
  • datagram security, 112
  • Datagram Transport Layer Security (DTLS), 112
  • date command, 15
  • dates
  • dd command
    • megabyte IO, 193
    • partition images, 94, 118
  • Debian systems, updating, 48, 129
  • debugfs command, 188
  • debugging, enabling, 27
  • debugging logs for libvirt, 31
  • declare command, 173, 175
  • declaring variables, 166
  • default base port in VNC, 78
  • default branches in repositories, 169
  • default configuration for BIND servers, 73
  • default delimiters, 55
  • default gateways
  • default paths, 176
  • default ports
  • default route, displaying, 15, 199
  • default.target unit, 191
  • default targets, displaying, 47
  • defaults line in/etc/fstab file, 24, 192
  • delimiters, setting, 81
  • deny policy for access control lists, 149
  • dependencies
    • displaying, 21, 51, 186–187
    • libraries, 48, 130
    • loaded modules, 20
    • loading, 5
  • depmod command
    • dependencies, 20
    • module comparisons, 35
  • detected hardware list, 157
  • /dev/disk/by-id directory, 24
  • /dev/disk/by-multipath directory, 35
  • /dev/disk/by-path directory, 25
  • /dev/disk/by-uuid directory, 33
  • /dev filesystem, 32
  • /dev/mapper directory, 26, 71
  • /dev/null directory, 81
  • /dev/nvme* directory, 70
  • /dev/pty device, 115
  • /dev/sda1 partition, 8, 94
  • /dev/sdX device, 50, 128
  • /dev/tty device, 84
  • devices
    • boot checking order, 12
    • collection of, 163
    • displaying names of, 50, 187
    • information on, 74
    • lsmod driver display, 6
    • pseudo-terminals, 115
  • df command
    • disk utilization, 19, 190
    • inodes, 134
    • report scale, 147
  • DHCP
    • configuration, 36
    • leases, 194
    • server system log, 71
  • dhcpd.conf file, 194
  • diff command, 77
  • dig command
    • mail server queries, 16, 137
    • server queries, 17
    • Start of Authority information, 18, 139
    • zone transfers, 19, 140, 193
  • digital signatures, 119
  • directories
    • copying, 55
    • creating, 55
    • finding, 54
    • large files on, 10, 134
    • listing, 167
    • log configuration, 121
    • permissions, 153
    • profiles, 112
    • removing, 54
    • traversal, 118
    • UFW configuration, 120
  • disabling
    • accounts, 196
    • Ctrl+Alt+Del keys, 110
    • hostname lookups, 148
    • logging, 35
  • disks
    • detecting, 128
    • GRUB Legacy configuration file, 8
    • preparing, 9
    • RAM, 20–21, 191
    • SATA, 50, 128, 194
    • space usage, 136
    • statistics, 146
    • unallocated space, 30
    • USB, 6, 129
    • utilization display, 19, 190
  • DISPLAY environment variable, 60
  • display port setting, 75
  • DisplayBase option, 75
  • dm-crypt
    • encryption, 197
    • volume configuration, 101
  • dmesg command
    • kernel ring buffer, 5, 71, 186
    • logs, 35
    • RAID adapters, 153
    • USB disks, 129
    • video cards, 83
  • dmidecode command, 155
  • dnf search command, 53
  • DNS
    • overriding, 18
    • server setting, 17, 137
    • SPF records, 19, 140
    • troubleshooting, 140
  • dnssec-keygen command, 103
  • do keyword
    • for loops, 175
    • until loops, 180
  • dollar signs ($)
    • command execution, 166
    • command-line arguments, 177
  • domains, information on, 13
  • dominfo command, 13
  • done keyword
    • for loops, 175
    • until loops, 180
  • dot (.) files, displaying, 117
  • dpkg command
    • package changes, 52
    • package information, 53, 132
  • dracut command, 21
  • drivers
    • displaying, 36
    • network interfaces, 36
  • DROP targets for iptables, 106
  • DTLS (Datagram Transport Layer Security), 112
  • du command
    • human-friendly format, 34
    • large files on directories, 10, 134
    • summary output, 157
  • dual-homed networks, 29
  • dumpe2fs command, 12, 23

E

  • -e option for file existence, 178
  • e2label command, 29
  • EC2 instances, 32
  • echo command
    • brace expansion, 164
    • forwarding, 107
    • newline characters, 169
    • paths, 166
    • variable display, 162
  • ECHO_REQUEST packets, 193
  • echo requests in ICMP, 147
  • echoing script names, 165
  • editing
    • /etc/sudoers file, 100
    • files, 114
  • EFI system partition, 5
  • efibootmgr command, 22
  • egrep command for finding users, 56
  • elif keyword, 181
  • email
    • address changes, 170
    • aliases, 66
    • destinations, 26, 108
    • statistics, 68
  • emailing logs, 97
  • emergency target, 197
  • empty passwords, 106
  • encrypted devices, listing, 23
  • encryption
    • authentication passwords, 156
    • dm-crypt command, 197
    • group passwords, 65
  • Enforcing mode in SELinux, 110
  • enumerating hosts database, 17, 137
  • env command
    • customized environments, 162
    • displaying, 132
    • environment variables, 167, 171
  • Environment key, 81
  • environment, printing, 165
  • environment variables
  • -eq operator for integer comparisons, 174
  • equal signs (=)
    • string comparisons, 165
    • variable comparisons, 176
  • error corrections
    • automatic, 134
    • swap partition, 134
  • error fixes with fsck command, 8, 191
  • esac sequence, 173
  • escape sequences
    • alerts, 174
    • carriage return and newline, 198
    • quotes, 163
  • /etc/apparmor.d directory, 112
  • /etc/apparmor.d/tunables directory, 119
  • /etc/apt/sources.list file, 52, 131
  • /etc/auto.master file, 70
  • /etc/bash.bash_logout file, 171
  • /etc/cron.allow file, 62
  • /etc/cron.daily directory, 63
  • /etc/cron.deny file, 96
  • /etc/crontab file, 63
  • /etc/crypttab file, 23
  • /etc/cups directory, 66
  • /etc/default/grub file
  • changes to, 8
  • timeouts, 7
  • /etc/default/keyboard file, 152
  • /etc/dhcpd.conf file, 36
  • /etc/exports file, 194
  • /etc/fail2ban directory, 106
  • /etc/fstab file
    • defaults line, 24, 192
    • device checking order, 12
    • filesystem information, 10
    • format, 11
    • mount command, 9
  • /etc/grub2.cfg, 28
  • /etc/gshadow file, 65
  • /etc/hosts.allow file, 101
  • /etc/hosts.deny file, 99
  • /etc/hosts file
    • correct line in, 17, 138
    • hostnames, 27
    • localhost addresses, 16
  • /etc/inetd.conf file, 100
  • /etc/init.d directory
    • linked files, 70
    • scripts, 46
  • /etc/inittab file
    • changes to, 49
    • Ctrl+Alt+Del keys, 110
    • runlevels, 70, 190
  • /etc/issue file, 102
  • /etc/issue.net file, 102
  • /etc/lib file, 130
  • /etc/localtime file, 189
  • /etc/logrotate.conf files, 97
  • /etc/logrotate.d directory, 121
  • /etc/mdadm.conf file, 26
  • /etc/modprobe.conf file, 30
  • /etc/modprobe.d directory, 21
  • /etc/motd file, 102
  • /etc/mtab file, 10
  • /etc/netplan directory, 34
  • /etc/network directory, 27
  • /etc/nologin file
    • login prevention, 141
    • PAM for, 104
  • /etc/nsswitch.conf file
    • authentication, 194
    • group information lookups, 16
  • /etc/pam.d directory, 104
  • /etc/passwd file
    • home directories, 103
    • output location, 55
    • user information, 61
    • usernames, 54
  • /etc/pki directory, 108
  • /etc/profile.d directory, 80
  • /etc/rc.d directory, 70
  • /etc/rc.local file, 79
  • /etc/rcS.d directory, 80
  • /etc/resolv.conf file
    • debugging setting, 27
    • DNS servers, 17, 137
    • local client services, 18, 139
  • /etc/rsyslog.conf file, 120
  • /etc/securetty file, 111
  • /etc/security/limits.conf file
    • process limits, 141
    • simultaneous logins, 142
  • /etc/services file, 98
  • /etc/shadow file
    • encrypted passwords, 156
    • password change dates, 69
    • passwords, usernames, and UUIDs in, 64
  • /etc/skel directory, 60, 189
  • /etc/ssh_known_hosts file, 100
  • /etc/sshd/sshd.conf file, 100
  • /etc/sudoers file
    • editing, 100
    • email destinations, 108
    • passwords, 99
  • /etc/sysconfig/network file, 33
  • /etc/sysconfig/network-scripts/ directory, 29
  • /etc/sysctl.conf file, 21
  • /etc/timezone file, 13
  • /etc/udev directory, 46, 186
  • /etc/ufw directory, 120
  • /etc/X11 directory, 82
  • /etc/X11/xorg.conf file, 60
  • /etc/yum.conf.d directory, 51, 130
  • /etc/yum.conf file, 52, 131
  • /etc/yum.repos.d directory, 72
  • ethernet bridges, creating, 36
  • ethtool command, 36
  • events, replaying, 78
  • exclude patterns in git command, 199
  • ExecStart option, 47
  • executable files
    • location, 58
    • permissions, 95
  • execute bit for scripts, 199
  • execution
    • commands. See command execution
    • scripts, 162, 164
    • of services on boot, 79
  • existence of files, 135, 178, 198
  • existing files with touch command, 55
  • exit codes
    • general errors, 180
    • success, 164
  • expansion of variables, 183
  • expiration of accounts, 69, 96, 190
  • export command
    • environment variables, 195
    • libraries, 130
    • variables, 166, 195
  • ext2 filesystems, 9
  • ext3 filesystems
    • vs. ext2 filesystems, 9
    • resizing, 31
  • extended hardware information, information on, 155
  • extensions
    • determining, 170
    • script execution, 164
  • extracting files from backups, 117

F

  • fail option for RAID arrays, 156
  • fail2ban system
    • configuration, 106
    • log file locations, 107
  • failed login attempts
    • account locking, 115
    • listing, 112
  • FAT filesystem for cluster servers, 79
  • fdisk command, 9
  • fg command, 56
  • FHS (Filesystem Hierarchy Standard)
    • mount points for removable media, 10
    • site-specific data, 9
  • fi keyword, 169
  • FibreChannel HBA, 149
  • file command, 170
  • file extensions
    • determining, 170
    • script execution, 164
  • files
  • Filesystem Hierarchy Standard (FHS)
    • mount points for removable media, 10
    • site-specific data, 9
  • filesystems
    • checking, 12
    • cluster servers, 79
    • information on, 10
    • labels, 29
    • remounting, 11
    • shared by NFS, 194
    • size, 31
    • times mounted, 10–11
    • type setting, 23
    • unmounting, 73
    • unreachable, 27
    • verification, 24
  • find command
    • directories, 54
    • files, 141–142
    • files owned by users, 66
    • inode numbers, 59
    • modified files, 57
    • users invoking sudo command, 57
  • finding zombie processes, 157
  • firewall-cmd command, 116
  • firewalld, zones for, 110
  • firewalls
  • for loops
  • foreground, bringing commands to, 56
  • formats for dates and times, 13, 175
  • formatting printing, 84
  • forwarding, enabling, 107
  • fprint package, 114
  • free command for memory usage, 133, 150, 190
  • fsck command
    • cleaned filesystems, 143
    • disk statistics, 146
    • error fixes, 8, 191
    • filesystem checking, 12
    • inodes, 134
    • root check skipping, 33
  • fstrim command, 25, 192
  • FTP, booting from, 28
  • functions
    • adding, 163
    • available at login, 60
    • example, 196
    • parentheses for, 173

G

  • G flag for route tables, 140
  • gateways, default
  • gdisk command
    • GUID partition tables, 111
    • partition names, 12
  • general errors, exit codes for, 180
  • getenforce command, 109
  • getent command
    • hosts database, 17, 137
    • users, 96
  • getfacl command, 111
  • getsebool command, 113
  • GIDs and UIDs, 64
  • git checkout command, 166, 182
  • git clone command, 195
  • git commit command, 180
  • git config command
    • configuration parameters, 179
    • email addresses, 170
  • GIT_DIR environment variable, 176
  • .git directory for repository metadata, 182
  • git log command, 168, 174
  • git ls-files command, 199
  • git merge command, 176
  • git pull command
    • positional parameters, 180
    • shared repositories, 180
  • git push command, 168
  • git remote show origin command, 177
  • git status command, 169
  • .gitignore file, 167
  • GnuPG key pairs, 100
  • gpg command
    • digital signatures, 119
    • key pairs, 100
    • public keyrings, 101
  • GPIO interface, 76
  • graphics cards configuration information, 60
  • grep command
    • file contents, 72
    • system log, 71
  • groupadd command, 80
  • groupdel command, 65
  • groupmod command, 62
  • groups
    • adding, 80
    • encrypted password information, 65
    • IP addresses, 150
    • lookup information, 16
    • membership lists, 155
    • names, 62
    • ownership, 94–95
    • printers, 68
    • removing, 65
    • su command access, 113
    • for users, 64
  • grub-install command
    • alternate directories, 23
    • MBR, 8
  • GRUB installed on MBR, 7–8
  • GRUB Legacy configuration file, 8
  • GRUB menu, 5, 186
  • grub-mkconfig command, 8
  • GRUB2 configuration files
    • new, 6
    • timeouts, 7
  • grub2-install command, 7
  • grub2-mkconfig command
    • booting location, 27
    • output to files, 7
  • grubx64.efi file, 23
  • guest logins, preventing, 135
  • GUID partition tables, information on, 111
  • gunzip command, 72
  • .gz files, 72
  • gzip command, 103

H

  • hangup signals for processes, 148
  • HAProxy server 400 response, 76
  • hard drives
    • detecting, 128
    • preparing, 9
  • hard links, 58
  • hardware
    • information on, 155
    • listing, 157
  • hardware clock
    • setting, 15
    • UTC time, 15
    • working with, 14
  • hashing algorithms for PKI, 113
  • head command, 54, 56
  • HEAD location, 166
  • HISTFILESIZE option, 195
  • history
  • hmac-md5 algorithm, 103
  • home directories
    • changing, 64
    • chroot, 103
    • copying files, 60
    • creating, 63
  • HOME environment variable, 173
  • horizontal tabs, 176
  • host command
    • authoritative name servers, 16
    • authorization name servers, 136
    • class type, 157
  • hostname characters, 27
  • hostname lookups
    • disabling, 148
    • preventing, 153
  • hostnamectl set-chassis command, 78
  • hosts
  • hotplug devices, USB, 47
  • HTTP 405 status code with TraceEnable, 85
  • http_access directive, 74
  • HTTP, booting from, 28
  • hwclock command for hardware clock
    • setting, 15
    • UTC time, 15
    • working with, 14
  • hypervisors
    • connections, 32
    • Type 1, 34

I

  • ibstat command, 148
  • ICMP
    • echo requests, 147
    • interface for, 16, 136
    • iptables rules, 107
    • ports, 98
  • iconv command, 32
  • id command, 65
  • id_rsa file, 99
  • IDs
  • if conditionals
    • end character, 169
    • file existence, 135
  • ifconfig command, 136
  • iftop command
    • hostname lookups, 153
    • interface setting, 156
    • network usage, 150
  • images for partitions, 94, 118
  • IN class for host command, 157
  • incremental backups, 114
  • inet protocols
    • default, 26
    • ip command, 144
  • InfiniBand devices, information on, 148
  • informational messages, 66
  • infrastructure as code, 162
  • infrastructure automation, 165, 178
  • inheriting permissions, 111
  • init command, 46
  • initialization files, shell execution without, 60
  • initializing partitions, 7, 131
  • inode index numbers
    • printing, 58
    • searching for files by, 59
  • inodes
    • byte-to-inode ratio, 149
    • partitions, 134
  • input, user, 172
  • INPUT chain policies, 106
  • insert mode for Vi editor, 57
  • insmod command, 21
  • install command, make command targets, 72
  • installing
  • integers, comparing, 174, 182
  • interactive logins, 135
  • interactive mode for NTP servers, 67
  • interfaces
    • displaying, 145
    • ICMP packets, 16
    • iftop, 156
    • information on, 136
    • netstat display of, 175
    • Raspberry Pi, 76
  • interpreter location, 171
  • interrupts, monitoring, 147
  • inventories
    • automated infrastructure, 174
    • device collections, 163
  • invoking Bash shell, 163
  • IO, scheduling, 150, 153
  • ioping command
  • iostat command
    • involuntary wait scenario, 178
    • megabyte display, 191
    • partition information, 19, 142
  • IP addresses
    • groups, 150
    • NTP servers, 66
    • ownership, 151
    • private, 136
  • ip command
    • default protocol, 26
    • newlines, 145
    • protocol family, 144
  • ip monitor command, 16, 137
  • ip route change command
    • commands following, 19
    • default gateways, 18, 138
  • ip route flush cache command, 19, 140
  • iperf command, 147
  • ipset command
  • iptables
    • ICMP traffic, 107
    • INPUT chain, 106
    • ipset software, 120
    • log entry limits, 106
    • Netfilter, 117
    • PREROUTING chain, 105
    • rules, 105–107
    • targets, 106, 108
    • UFW configuration, 120
  • iptables-save command
  • iptraf command, 150
  • IPv6 localhost addresses, 16
  • IRQ assignments, viewing, 46, 186
  • ISOLINUX bootloader, 22
  • itop command, 147
  • iw dev command, 71
  • iwconfig command, 26, 83

J

  • JAVA_PATH environment variable, 195
  • JavaScript Object Notation (JSON) format, 28
  • jobs
    • background tasks, 133
    • removing, 63, 196
    • scheduled, 189
  • journalctl command
    • disk space, 136
    • log entries, 96, 121
    • log-file entries, 196
    • reverse output, 197
  • journald.conf file, 97
  • journaling in ext3 filesystems, 9
  • JSON (JavaScript Object Notation) format, 28

K

  • Kerberos authentication
  • KerberosAuthentication option, 121
  • kern facility, 96
  • kernel
    • installing, 30
    • message logs, 96
    • parameters, 148
    • udev events, 70
    • updating, 52, 131
    • upgrading, 69
    • version, 52, 131
  • kernel-install command, 30
  • kernel modules
    • custom commands, 30
    • installing, 20
    • loaded, 5
    • location, 28
  • kernel ring buffer
    • clearing, 71
    • kernel panic messages, 28
    • viewing, 5, 186
  • keyrings in gpg, 101
  • keys and key pairs
  • kickstart
    • and anaconda, 31
    • booting, 35
  • kill command
    • BIND reloading, 77
    • processes, 56–57, 148
  • killall command, 133
  • killing processes, 133, 200
  • klist command, 112
  • kmag command, 61

L

  • labels for filesystems, 29
  • LACP protocol, 33
  • LANG environment variable, 14, 179
  • large files on directories, 10, 134
  • last command for logs, 68
  • lastb command for failed login attempts, 112
  • latency
    • diagnosing, 151
    • ping command, 147
  • LC_ALL environment variable, 14, 178
  • LC_MONETARY environment variable, 14, 181
  • LC_TIME environment variable, 13, 175
  • LDAP
  • ldconfig command, 48, 129, 200
  • ldd command, 48
  • leases, DHCP, 194
  • legal disclaimer information, suppressing, 156
  • less command, 58
  • /lib/systemd/system folder, 49
  • libraries
  • LIBVIRT_DEBUG, 31
  • libvirt for debugging logs, 31
  • limits
    • PAM, 122
    • password age, 121
    • processes, 141
    • simultaneous logins, 142
    • users, 99
  • lines, printing, 54
  • linked files, 70
  • links cache wireless device status, 71
  • links for shared libraries, 48, 129
  • --list option for configuration parameters, 179
  • ln command
    • symlinks, 58
    • time zones, 14
  • load average, 133, 142, 200
  • load balancing in bonding scenarios, 35
  • loaded modules, displaying
    • currently loaded, 20
    • kernel, 5
  • loading modules and dependencies, 5
  • local authentication for encrypted passwords, 156
  • local client services, enabling, 18, 139
  • local command for variables, 165
  • local servers, daemons on, 149
  • local time zones, 13
  • local variables, indicating, 165
  • local# facilities for custom logs, 67
  • locale
    • currency, 181
    • translations bypassing, 14, 179
    • variable reconfiguration, 14, 178
  • localectl command, 29
  • localhost in IPv6, 16
  • locate command for database updates, 59
  • locking accounts, 115
  • locking out password-based logins, 63
  • --log-prefix option for iptables, 108
  • logged-in users, 68–69, 142
  • logical volumes
    • creating, 7, 131, 192
    • directories, 71
    • information on, 26
    • logical creation order, 8
  • logins
    • 3D acceleration, 75
    • console, 111
    • environment, 101
    • interactive, 135
    • preventing, 104, 141
    • simultaneous, 142
    • user information, 73
  • logouts
    • commands executed on, 171
    • processes running after, 85
    • users, 177
  • logpath option, 107
  • logrotate command, 121
  • logrotate configuration file, 97
  • logs and log files
    • authentication and authorization, 115
    • compression, 97
    • custom, 67
    • disabling, 35
    • emailing, 97
    • entry display, 120–121
    • entry limits, 106
    • entry parsing, 196
    • journals, 97
    • kernel messages, 96
    • last command, 68
    • locations, 107
    • output from, 76
    • output to, 163
    • packets, 122
    • systemd-journald service, 96
    • watching, 94
  • loops
  • lpr command
    • capturing messages, 196
    • print queues, 67
  • lpxelinux.0 file, 28
  • ls command
    • dot files, 54, 117
    • example, 50
    • filters, 167
    • hard links, 58
    • inode index numbers, 58
    • ownership, 112, 149
    • partitions, 128
    • permissions, 59, 112
    • SELinux, 119
    • symbolic links, 186
  • lsattr command, 156
  • lsblk command
    • boot partitions, 72
    • partition information, 36
  • lsdev command, 74
  • lshw command, 157
  • lsmod command
    • device drivers, 6
    • loaded modules, 5, 20
  • lsof command, 141
  • lspci command
    • listing, 187
    • numeric codes and device names, 50, 187
  • lsusb command
    • Bluetooth devices, 85
    • USB connections, 48
    • USB devices, 46, 128
  • -lt operator, 181
  • LUKS
    • encryption, 197
    • key-derivation function, 101
  • LUNs
    • from Fibre Channel, 25
    • paths, 25
  • lvcreate command, 7, 131, 192
  • LVM
    • logical volumes, 7, 131
    • partitions, 7, 131
  • lvmdiskscan command, 8, 132
  • lzma extension, 94

M

  • MAC addresses
    • new entries, 145
    • removing, 144
  • machine type setting, 78
  • magnification functionality, 61
  • mail command for STDIN messages, 73
  • mail option for emailing logs, 97
  • mail queues
    • directories, 66
    • Postfix servers, 67
  • mail servers
    • email aliases, 66
    • queries, 16, 137
  • mail storage, 187
  • MAILADDR option, 26
  • mailstats command, 68
  • mailto option, 108
  • make command
    • commands and relationships used with, 72
    • targets, 72
  • make oldconfig command, 69
  • Makefile name, 72
  • Master Boot Record (MBR)
    • GRUB on, 7–8
    • partition information, 22
    • primary partitions, 6
  • master branch in repositories, 169
  • matching files, 177
  • MATE desktop environment, 76
  • max-lease-time option, 194
  • maximum mount count, 199
  • maxlogins option, 142
  • MBR (Master Boot Record)
    • GRUB on, 7–8
    • partition information, 22
    • primary partitions, 6
  • mdadm command
    • arrays, 25, 192
    • email, 26
    • polling interval, 145
    • RAID arrays, 26
  • /media file, 10
  • membership lists for groups, 155
  • memory usage
  • merge command for repositories, 164
  • merge conflicts, rolling back, 176
  • messages
    • capturing, 196
    • informational, 66
    • kernel logs, 96
    • netlink, 16, 137
    • repositories, 168
    • for users, 102
    • warning, 103
    • welcome, 61
  • metadata in repositories, 182
  • mixer volumes, 82
  • mkdir command
  • directories, 55
  • repositories, 163
  • mke2fs command
    • bad blocks, 147
    • changing, 149
    • filesystem type, 23
  • mkfs.btrfs command, 11
  • mkinitrd command, 20, 191
  • mkswap command, 134, 192
  • modified files, finding, 57
  • modifying files, 103
  • modinfo command, 20
  • modprobe command, 5
    • dependencies, 21, 186
    • kernel module, 20
    • removing modules, 21
  • modules
    • blacklist information, 21
    • comparing, 35
    • dependencies, 21, 186
    • inserting, 21
    • loading, 5
    • removing, 21
    • unloading, 6, 35
  • monitoring
    • interrupt usage, 147
    • performance, 69
    • processes, 188
  • monitors
    • configuration, 60, 81
    • X11, 81
  • more command, 84
  • mount command
    • /etc/fstab files, 9
    • mount process simulation, 199
    • partitions, 22
    • USB devices, 12
    • USB disks, 6
  • mount count maximum, 199
  • mount points for removable media, 10
  • mounted filesystems
    • displaying, 32
    • /etc/mtab file, 10
  • moving
    • files, 57
    • positional parameters, 180
  • mtr command, 145
  • multibyte representation, 13, 189
  • multipath command, 25
  • multiple commands, running, 167, 182
  • mv command
    • overwriting files, 55
    • text files, 57
  • MX records, 193
  • MySQL default ports, 82

N

  • nagios software, 69
  • NAME option for network adapters, 82
  • name resolution
  • name servers
    • ports, 97
    • querying, 16
  • named.conf file, 73
  • names
    • changing, 65
    • groups, 62
    • network adapters, 82
    • partitions, 12
  • nameserver line, 17
  • Nano editor, 83
  • NAT vs. bridging, 30
  • nc command, 139
  • net command, 104
  • NetBIOS name service requests, 74
  • netcat command, 139
  • Netfilter firewalls, 117
  • netlink messages, 16, 137
  • netstat command
    • current default route, 15, 199
    • hostname lookups, 148
    • interface information, 175
    • routing tables, 157
    • services and sockets, 17, 138
  • network adapter names, 82
  • network bonding, 30
  • network interfaces, drivers, 36
  • Network Manager, 150
  • networks
    • component authentication, 117
    • configuration, 29
    • configuration saving, 33
    • throughput measuring, 147
    • usage displaying, 150
  • new files, permissions for, 95
  • newaliases command, 66
  • newlines
    • echo command, 169
    • escape characters, 198
    • removing, 145
  • nice command, 133
  • nmap command
    • name resolution, 145
    • open ports, 141–142
    • Xmas scans, 146
  • nmbd daemon, 74
  • nmcli command, 150
  • --no-commit option for shared repositories, 180
  • nocompress option for logs, 97
  • nohup command, 85
  • non-interactive mode
    • command execution in, 99
    • sudo command, 119
  • non-swap partitions, 132
  • NOPASSWD option, 99
  • --norc option for shell execution without initialization files, 60
  • nslookup command, 36, 154
  • NTP
    • interactive mode, 67
    • IP addresses, 66
    • ports, 108
  • ntpq command, 67
  • numeric codes, displaying, 50, 187
  • NXDOMAIN message, 140

O

  • o command in Vi editor, 57
  • octal notation for permissions, 120
  • open ports, scanning for, 141–142
  • open source package for Remote Desktop Protocol, 82
  • OpenSSH
    • empty passwords, 106
    • login allowing, 108
    • SSH client logins, 74
  • openssl command
    • certificate authority servers, 73
    • Certificate Signing Requests, 77
  • OpenVPN
    • network access, 74
    • ports, 106
  • Orca screen reader, 61
  • orchestration
    • agentless infrastructure, 183
    • agents, 164, 198
    • Ansible package, 162
  • --origin option for repositories, 177
  • output
    • escape characters, 163
    • to log files, 163
    • logging, 76
    • redirecting, 7, 81, 170
    • variables, 177
  • output files, setting, 80
  • OVA files, 34
  • overwriting files, 55
  • OVF templates, 29
  • ownership
    • changing, 95, 118
    • deleted accounts, 66
    • displaying, 112, 149
    • groups, 94–95
    • inherited, 152
    • IP addresses, 151

P

  • packages
  • packets
  • pager, more command for, 84
  • pam_cracklib.so module, 105
  • pam_limits.so module, 122
  • pam_listfiles.so module, 122
  • pam_nologin.so module, 104
  • pam_tally2 module, 115
  • pam_unix.so module, 105
  • parameters, positional, 180
  • parentheses () for functions, 173
  • parsing log-file entries, 196
  • parted command, 12
  • partition/mounted/var directory, 50, 187
  • partition tables, updating, 151
  • partitions
    • changing, 12
    • displaying, 128
    • EFI system, 5
    • GRUB Legacy configuration file, 8
    • identifying, 6
    • images, 94, 118
    • information on, 34, 36
    • initializing, 7, 131
    • inodes, 134
    • listing, 36
    • MBR, 22
    • names, 12
    • non-swap, 132
    • RAID arrays, 24
    • swap, 6, 134, 143, 192
    • UUIDs, 11
  • partprobe command, 151
  • passwd command, 64
  • password-based logins, locking out, 63
  • passwords
    • age limits, 121
    • boot prevention, 114
    • bootloaders, 110
    • change dates, 64, 69
    • empty, 106
    • file, 64
    • local authentication, 156
    • PAM authentication, 105
    • recovering, 128
    • skipping, 99
    • strength, 105
  • paste command delimiters, 81
  • patch command for file backups, 198
  • patch files, whitespaces in, 197
  • paths
  • PBKDF2 function, 101
  • pcap format for traffic, 151
  • pci-0000 file, 25
  • PEM format, 105
  • performance
    • CPU, 191
    • graphing, 143
    • historical data, 151
    • monitoring, 69
    • polling interval, 145
  • permissions
    • bash scripts, 154
    • directories, 153
    • displaying, 94
    • files, 112
    • inheriting, 111
    • new files, 95
    • octal notation, 120
    • rsync command, 198
    • suid bit, 95
    • symlinks, 59
    • tar command, 197
    • writing, 154
  • Permissive mode in SELinux, 109
  • PermitEmptyPasswords option, 106
  • PermitRootLogin option, 74
  • persistent volumes, 29
  • pgrep command, 132
  • physical volumes
    • information on, 144
    • logical volumes from, 8
    • searches, 8, 132
  • pidof sshd command, 148
  • ping command
    • bypassing routing tables, 198
    • ECHO_REQUEST packets, 193
    • emulating, 18, 139
    • ICMP echo requests, 147
    • ICMP packets, 136
    • latency, 147
    • packet policies, 146
    • querying, 16
  • PKI hashing algorithms, 113
  • pkill command, 153
  • Pluggable Authentication Modules
    • authorization and authentication, 122
    • configuration, 104
    • failed login attempts, 115
    • login prevention, 104
    • password authentication, 105
    • password strength, 105
    • policies, 149
    • required, 109
    • user limits, 122
  • policies
    • INPUT chain, 106
    • PAM, 149
    • SELinux configuration, 109
  • polling interval for performance, 145
  • port forwarding in SSH, 76
  • port-to-protocol translations, 98
  • ports
    • configuring, 97
    • CUPS administrative web interface, 67
    • CUPS printing daemon, 152
    • FibreChannel HBA, 149
    • firewalls, 68
    • ICMP, 98
    • LDAP, 122, 189, 196
    • MySQL, 82
    • name servers, 97
    • NTP, 108
    • open, 141–142
    • OpenVPN, 106
    • slapd daemon, 104
    • SMTP traffic, 97
    • Squid, 104
    • SSH, 122, 138
    • telnet, 119
    • VNC, 78
    • well-known, 121
  • positional parameters, moving, 180
  • Postfix
    • mail queues, 67
    • TLS configuration formats, 105
  • postqueue command, 67
  • pound signs (#)
    • command-line arguments, 177
    • comments in scripts, 164
  • PREROUTING chain, 105
  • primary partitions, 6
  • printenv command, 165
  • printer groups, 68
  • printf command, 84
  • printing
    • awk command, 195
    • completed print jobs, 67
    • environment, 165
    • formatting, 84
    • inode index numbers, 58
    • libraries, 200
    • lines, 54
    • lists, 172
    • ports, 152
    • print queues, 67
  • priority
  • private addresses, 15, 136
  • private keys
    • Apache servers, 83
    • certificate authority servers, 73
    • SSH, 118, 120
    • ssh-agent, 110
  • privileges, minimum, 95
  • /proc/bus/usb directory, 50
  • /proc filesystem, 47
  • /proc/meminfo file, 146
  • /proc/mounts file, 32
  • /proc/partitions file, 34
  • procedure infrastructure automation, 178
  • processes, 158
  • .profile file for time zones, 14, 181
  • profiles
  • progress indicators, 10, 188
  • ps auwx command, 118
  • ps aux command, 112
  • ps command
    • memory usage, 157, 200
    • SELinux contexts, 115
    • uninterruptible sleep, 152
    • zombie processes, 157
  • PS1 environment variable, 172
  • pseudo-terminals devices, 115
  • public keyrings for gpg, 101
  • public keys in SSH, 98, 107, 120
  • pubring.gpg file, 101
  • pull command for repositories, 162
  • purging caches, 33
  • push command for network access, 74
  • pvcreate command, 7, 131
  • pvdisplay command, 25, 144
  • pvscan command, 144
  • PXE boot, 23
  • pxelinux.0 file, 23

Q

  • query destinations, changing, 154
  • question marks (?) with less command, 58
  • quotacheck command
    • file creation, 135
    • user quotas, 59
  • quotas
    • enabling, 135
    • usage display, 59

R

  • escape characters, 198
  • RAID arrays
    • adapter detection, 153
    • mdadm command, 26
    • partitions, 24
    • removing disks from, 156
  • RAM disks, 20–21, 191
  • Raspberry Pi interfaces, 76
  • raw devices, 30
  • rc file runlevels, 70
  • read command for user input, 172
  • read I/O requests, displaying, 34
  • read-only variables
    • creating, 175
    • displaying, 170
  • readonly command, 170
  • rebooting, 46
  • reconfiguring locale variables, 178
  • recovering passwords, 128
  • recursive changes in chmod command, 169
  • redirection
  • regions in time zones, 13, 189
  • REJECT targets for iptables, 106
  • relative paths, 30
  • reloading BIND, 77
  • Remote Desktop Protocol, 82
  • remote names, obtaining, 177
  • remounting filesystems, 11
  • removable media, mount points for, 10
  • removing
    • blocks, 25, 192
    • cron jobs, 196
    • directories, 54
    • environment variables, 171
    • files, 84, 102
    • groups, 65
    • jobs, 63
    • MAC addresses, 144
    • modules, 21
    • newlines, 145
    • users, 62
  • renice command, 148
  • replaying events, 78
  • reports scale, 147
  • repositories
    • changes to, 164
    • cloning, 177, 195
    • copying, 169
    • creating, 163
    • default branches, 169
    • file versions, 167
    • messages, 168
    • metadata, 182
    • packages, 131
    • retrieving, 165
    • retrieving objects from, 162
    • shared, 180
    • URLs, 72
    • Yum, 130
  • repquota command, 59
  • requests
  • reserved blocks, displaying, 12
  • resize2fs command, 31
  • resizing filesystems, 31
  • restarting
    • Apache servers, 75
    • CUPS, 68
    • processes, 57, 133
  • restorecon command, 114
  • rm command, 54
  • rmmod command, 6, 35
  • rndc command
    • authentication, 103
    • BIND name servers, 79
  • rolling back merges, 176
  • root user
    • console logins, 111
    • SSH logins, 116
    • UIDs, 109
  • route add command
  • route command
    • flags, 19
    • name resolution, 144
  • routes
  • routing tables
  • rpm command
  • rpm kernel command, 52, 131
  • rpm package file output location, 48
  • rpm2cpio output location, 48
  • RSA hashing algorithms, 113
  • rss column for memory usage, 157
  • rsync command
    • archive mode, 71
    • file modifications, 103
    • file removal, 102
    • file size, 193
    • options, 108
    • permissions, 198
    • synchronization process, 103
  • rsyslog command, 120
  • rules
    • iptables, 105–107
    • reloading, 75
  • runlevel command, 49
  • runlevels
    • displaying, 47, 49
    • rc files, 70
    • setting, 79
    • single user mode, 46, 190
  • --runtime-to-permanent option, 116

S

  • Samba for NetBIOS name service requests, 74
  • SANs (storage area networks), 9
  • sar command
    • CPU performance, 191
    • historical performance data, 151
  • SATA (Serial ATA) disks
  • scale, report, 147
  • scheduled jobs, 189
  • scheduling
  • scp command, 85, 117
  • screen command, 133
  • screen reader, Orca, 61
  • Screen section for graphics card and monitor configurations, 60
  • scripts
    • directories, 27
    • execute bit, 199
    • execution, 162, 164
    • file extensions, 164
    • file removal, 84
    • permissions, 154
    • services, 46
    • storage, 80
    • terminating, 175
  • scrolling logs, 94
  • SCSI devices
    • host adapter scans, 156
    • support per bus, 49, 129
  • search line for local client services, 18, 139
  • searches
    • files, 141–142
    • package caches, 52, 131
    • packages, 51, 188
    • physical volumes, 8, 132
  • SeatDefaults for guest logins, 135
  • security bulletins, 116
  • sed command, 53
  • SELinux
    • access denials, 155
    • booleans list, 113
    • configuration policies, 109
    • contexts, 113, 115, 119, 152
    • Enforcing mode, 110
    • Permissive mode, 109
  • SELINUXTYPE option, 109
  • semicolons (;)
    • case statement, 178
    • chaining commands, 77, 174
  • seq command, 172
  • Serial ATA (SATA) disks
  • server command for query destinations, 36, 154
  • servers
    • containers, 75
    • queries, 17
    • site-specific data, 94
  • service accounts UIDs, 155
  • service apache2 restart command, 75
  • service reload command, 81
  • service status command, 77
  • service units, listing, 50, 187
  • services
  • sestatus command, 120
  • set command for output redirection, 170
  • setenforce command, 110
  • setsebool command, 111
  • SFTP
    • file transfers, 116
    • kickstart booting, 35
  • sha1sum utility, 118
  • SHA256withRSA option, 113
  • shared IDs, 114
  • shared libraries
  • shared repositories, changes to, 180
  • shebang lines for interpreter location, 171
  • shells executed without initialization files, 60
  • shift command for positional parameters, 180
  • Shift key
    • GRUB menu, 5, 186
    • sticky keys, 61
  • shim.efi bootloader, 22–23
  • shims for UEFI, 23
  • shutting down services, 78
  • SIGKILL signal, 157
  • SIGTERM signal, 200
  • simultaneous login limits, 142
  • single-user mode
    • booting, 5
    • passwords, 128
    • runlevels, 46, 190
    • setting, 49
  • site-specific data
    • FHS, 9
    • servers, 94
  • size
    • /boot partition, 7
    • dumps, 24
    • files, 154, 193
    • filesystems, 31
    • journal logs, 97
    • partitions, 12
    • requests, 155
  • size column for memory usage, 157
  • slapd.conf file, 122
  • slapd daemon, 104
  • SMTP traffic ports, 97
  • snapshots for packets, 146
  • SNMP servers firewall ports, 68
  • sockets display, 17, 26, 138, 192
  • software
  • software tokens in two-factor authentication, 110
  • sort command for unique items, 57
  • sort order in top command, 143
  • source code, committing, 168
  • source command
  • spawned windows in SSH sessions, 60
  • SPF record for DNS queries, 19, 140
  • Spice remote access, 79
  • SQL commands, reading, 168
  • square brackets [ ]
    • file matching, 177
    • while loops, 173
  • Squid
    • access control lists, 73–74
    • ports, 104
  • /srv directory, 9, 94
  • ss command
  • SSD disk location, 70
  • SSH
    • agentless infrastructure orchestration, 183
    • authentication keys, 190
    • connections, 197
    • hosts, 111
    • Kerberos authentication, 121
    • keys, 98–99, 107, 120, 194
    • login prevention, 141
    • port forwarding, 76
    • ports, 122, 138
    • private keys, 118
    • root user logins, 74, 116
    • spawned window sessions, 60
    • synchronization process, 103
    • ufw traffic, 116
    • X session connections, 61
  • ssh-add command, 110
  • ssh-agent command, 110
  • ssh.conf file, 109
  • ssh-copy-id command, 107
  • ssh-keygen command, 98, 122, 194
  • sshd.conf file, 109
  • sshd_config file, 116
  • SSL
    • certificate authority servers, 73
    • configuration, 108
    • private keys, 83
    • VPN clients, 113
  • SSLCertificateKeyFile directive
    • Apache servers, 83
    • configuration, 104
  • SSLEngine option, 104
  • Start of Authority information, 18, 139
  • startup commands for udev devices, 80
  • STDERR, redirecting, 56, 84, 170, 179
  • STDIN
  • STDOUT
  • steal column in involuntary wait scenario, 178
  • sticky bits, enabling, 95
  • sticky keys, enabling, 61
  • stopping
    • daemons, 81
    • processes, 56
    • services, 69, 78
  • storage
    • blob, 31
    • host caches, 100
    • libraries, 130
    • mail, 187
    • network configurations, 33
  • storage area networks (SANs), 9
  • strings, comparing, 165
  • su command
    • access restrictions, 113
    • login environment, 101
    • non-interactive sessions, 99
  • subshells, command execution in, 166
  • substitution operation, 53
  • sudo command
    • accounts, 96
    • credentials, 190
    • non-interactive mode, 119
    • specific user, 99
  • sudoedit command, 114
  • suid bit for permissions, 95
  • summary output with du command, 157
  • suspending daemons, 83
  • swap partitions
    • creating, 192
    • error corrections, 134
    • identifying, 6
    • skipping, 143
  • swap space
    • activating, 155
    • deactivating, 143
    • description, 130
    • displaying, 133, 190
    • information on, 143
  • swapoff command, 143
  • swapon command, 143, 155
  • switch support in bonded-link aggregation, 33
  • symlinks
    • displaying, 186
    • files, 28, 58
    • permissions, 59
    • World Wide Identifiers, 24
  • synchronization process in SSH, 103
  • /sys/block file, 153
  • /sys/class/fc_host directory
    • FibreChannel HBA, 149
    • WWN for Fibre Channel, 71
  • /sys/class/scsi_host/hostN/scan file, 156
  • sysctl command
    • boot values, 21
    • kernel, 148
    • parameters, 152
    • settings display, 20, 200
  • syslog level for informational messages, 66
  • system BIOS for hard drive detection, 128
  • system files, changes to, 117
  • system log for DHCP server, 71
  • system users, creating, 65
  • system-wide cron files, 63
  • systemctl command for killing processes, 200
  • systemctl daemon-reload command, 70
  • systemctl disable command, 69
  • systemctl enable command, 47
  • systemctl get-default command, 47
  • systemctl isolate command, 49
  • systemctl list-units command, 50
  • systemctl mask command, 84
  • systemctl restart command, 68
  • systemctl status command, 49, 77, 187
  • systemctl stop command, 81
  • systemd-analyze command, 76
  • systemd-journald service, 96
  • systemd system
    • configuration changes, 70
    • configuration files, 49
    • environment variables, 81
    • journal, 96
    • programs to execute, 47
    • service units, 187
    • targets, 197
  • SystemMaxFileSize option, 97
  • systemwide time zones, 14
  • SysVinit service scripts, 46

T

  • escape sequence, 176
  • tabs
    • cut command delimiter, 55
    • horizontal, 176
  • TACACS+ authentication, 117
  • tail command
    • lines printed, 54, 56
    • logs, 94
  • tar command
    • excluding files, 102
    • packages, 53
    • permissions, 197
    • tar file creation, 101
    • uncompressing files, 102
  • targets
  • TCP
    • CUPS administrative web interface portd, 67
    • SMTP traffic ports, 97
    • three-way handshakes, 98
    • wrappers, 99
  • TCP SYN packets and open ports, 142
  • tcpdump command
    • interfaces, 145
    • packet snapshots, 146
  • tcptraceroute command, 151
  • telinit command, 49
  • telnet ports, 119
  • terminals for processes, 84
  • terminating scripts, 175
  • test command arguments, 173
  • /tftpboot directory, 23
  • .tgz file extension, 53
  • third-party logging agents, 112
  • three-way handshakes, 98
  • 3D acceleration, 75
  • ticket caches in Kerberos authentication, 112
  • tilde character (~) for home directories, 173
  • time zones
  • timedatectl command, 13
  • timeouts
    • GRUB2 configuration files, 7
    • troubleshooting, 151
  • times
    • command execution time, 31
    • formats, 13, 175
    • setting, 15
  • timestamps, changing, 55
  • TMOUT environment variable, 177
  • tokens in two-factor authentication, 110
  • top command
    • process monitoring, 188
    • sort order, 143
  • touch command
    • existing files, 55
    • login prevention, 141
  • tr command, 83
  • TraceEnable setting, 85
  • tracepath command, 139
  • traceroute command
    • live updates, 145
    • TCP SYN packets in, 137
    • vs. tracepath, 139
    • unreachable hosts, 146
  • traffic
    • determining, 150
    • pcap format, 151
    • preventing, 18, 139
  • transferring files, 116
  • Transport mode for VPNs, 115
  • traversal of directories, 118
  • troubleshooting
    • connections, 140
    • third-party logging agents, 112
  • tshark command, 151
  • tune2fs command
    • error corrections, 9, 134
    • extended options, 25
    • maximum mount count, 199
    • times filesystems mounted, 10–11
  • two-factor authentication tokens, 110
  • Type 1 hypervisors, 34
  • type command, 171
  • TZ line, 14, 181

U

  • Ubuntu distribution Unity desktop, 80
  • udev devices
    • configuration, 46, 186
    • network adapter names, 82
    • startup commands, 80
  • udev events, 70
  • udevadm control command, 75
  • udevadm monitor command, 70
  • udevadm trigger command, 78
  • UDP for OpenVPN, 106
  • $UDPListen option, 97
  • UEFI
    • bootloaders, 22
    • passwords, 114
    • shims, 23
  • ufw allow command, 116
  • UFW configuration, 120
  • UIDs
    • authentication servers, 64
    • root account, 109
    • service accounts, 155
  • ulimit command
  • umask command, 94
  • umount command
    • remounting filesystems, 11
    • unmounting filesystems, 73
    • unreachable filesystems, 27
  • unalias command, 178
  • unallocated disk space, 30
  • uncompressing files
    • .gz files, 72
    • lzma files, 94
    • tar command, 102
  • uninterruptible sleep process state, 152
  • Unity desktop, 80
  • unlink command, 84
  • unloading modules, 6, 35
  • unreachable hosts with traceroute command, 146
  • until loops
    • beginnings and ends, 180
    • vs. while, 182
  • update-grub command, 6
  • updatedb command, 59
  • updating
    • Debian systems, 48
    • kernel, 52, 131
    • package caches, 52
    • packages, 130
    • partition tables, 151
    • software, 129
    • traceroute, 145
  • upgrading kernel, 69
  • uptime command for load average, 133, 200
  • URLs for package repositories, 72
  • USB devices
    • Bluetooth, 85
    • connection points, 129
    • connections, 48
    • hotplug, 47
    • listing, 46, 128, 186
    • mounting, 6, 12
    • storage, 50
  • user accounts. See accounts
  • useradd command
    • disabling accounts, 196
    • groups, 64
    • home directories, 63
    • system users, 65
  • userdel command, 62
  • usermod command
    • expiring accounts, 69
    • home directories, 64
    • password-based logins, 63
    • printer groups, 68
    • user names, 65
  • usernames
    • changing, 65
    • IDs, 80
    • listing, 54
  • users
    • automatic logouts, 177
    • configuration files for login order, 60
    • cron availability, 62
    • cron scheduled tasks, 96
    • files owned by, 66
    • groups, 64
    • information on, 65
    • input by, 172
    • limits, 99
    • listing, 96
    • logged in, 68–69, 142
    • login allowing, 108
    • login information, 73
    • login limits, 122
    • messages for, 102
    • printer groups, 68
    • process limits, 141
    • quotas, 59, 135
    • readable information, 61
    • removing, 62
    • system, 65
  • /usr/lib/firewalld/zones directory, 110
  • /usr/lib/modules file, 28
  • /usr/share/zoneinfo directory, 13, 189
  • usrquota command, 135
  • UTC time for hardware clock, 15
  • UTF-8 encoding for multibyte representation of characters, 13, 189
  • UUIDs
    • obtaining, 33
    • partitions, 11

V

  • values, displaying, 20
  • /var/log/kern.log file, 28
  • /var/log/secure file, 116
  • /var/qmail/queue directory, 66
  • /var/spool/cron/crontabs directory, 62
  • /var/tmp/abrt directory, 78
  • variables
    • adding, 163
    • availability, 195
    • comparing, 176
    • declaring, 166
    • displaying contents, 162
    • environment. See environment variables
    • expansion, 183
    • local, 165
    • output, 177
    • read-only, 170, 175
    • setting, 174
  • verbose output in installations, 51, 187
  • versions
  • VFS (virtual filesystem), 31
  • vgscan command, 144
  • Vi editor
    • insert mode, 57
    • saving work, 56
  • video cards, determining, 83
  • video devices Spice remote access, 79
  • <video> stanza for Spice remote access, 79
  • virsh command
    • domain information, 13
    • hypervisors, 32
  • virt-install tool, 33
  • virtual filesystem (VFS), 31
  • virtual machines, installing, 33
  • <VirtualHost> directive, 77
  • visudo editor, 100
  • vmlinux, 28
  • vmlinuz, 28
  • vmstat command
    • blocks, 142
    • IO wait statistics, 200
  • VNC
    • default base port, 78
    • services, 78
  • volumes
    • creation order, 8
    • information on, 25, 144
    • logical, 71, 131
    • persistent, 29
    • searches, 132
  • VPNs
    • SSL-based clients, 113
    • Transport mode, 115

W

  • w command for logged in users, 68–69, 142
  • wa statistic for IO wait time, 200
  • warning messages, suppressing, 103
  • watching logs, 94
  • WAYLAND_DISPLAY environment variable, 74
  • Wayland sessions, 74
  • wc command, 54
  • web servers, enabling, 59
  • welcome message, setting, 61
  • Welcome section, 61
  • well-known ports, 121
  • wget command, 76
  • wheel group for su command access, 113
  • whereis command, 58
  • which command, 58
  • while loops
  • whitespaces in patch file, 197
  • who command, 73
  • whoami command, 80
  • whois command
    • IP address ownership, 151
    • legal disclaimer information, 156
  • wildcard matches in /etc/hosts.allow file, 101
  • windows, information on, 188
  • wireless devices
    • link status, 71
    • parameters, 26, 83
  • World Wide Identifiers (WWIDs)
    • /dev/disk/by-multipath directory, 35
    • symlinks, 24
  • :wq command in Vi editor, 56
  • WWN for Fibre Channel, 71

X

  • X server connections, 135
  • X sessions, SSH connections in, 61
  • X11Forwarding option
    • SSH connections, 61
    • X11 forwarding, 100
  • xfs_check command, 24
  • xfs_growfs command, 11
  • xfs_info command, 11
  • xfs_metadump command, 10, 188
  • xfsdump command, 24
  • xfsrestore command, 24
  • xhost command, 135
  • Xmas scans, 146
  • XML standard for OVF templates, 29
  • xorg.c file, 82
  • xrdp package, 82
  • xwininfo command, 188
  • xz command, 94

Y

  • YAML format
    • EC2 instances, 32
    • /etc/netplan directory, 34
    • extension, 179
  • .yml extension, 179
  • yum deplist command, 51, 187
  • yum install command, 48, 129
  • Yum repositories, 51, 130
  • yum search command
    • package caches, 52
    • partitions, 131
  • 0xFD partitions for RAID arrays, 24

Z

  • zip command, 118
  • zombie processes, finding, 157
  • zone transfers, 19, 140, 193
  • zones, firewalld, 110
  • zypper info command, 53
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