206: System Maintenance

206.1 Make and install programs from source (weight: 2)

Candidates should be able to build and install an executable program from source. This objective includes being able to unpack a file of sources.

Key Knowledge Areas:

• Unpack source code using common compression and archive utilities.

• Understand basics of invoking make to compile programs.

• Apply parameters to a configure script.

• Know where sources are stored by default.

The following is a partial list of the used files, terms and utilities:

• /usr/src/

• gunzip

• gzip

• bzip2

• xz

• tar

• configure

• make

• uname

• install

• patch

Undrestanding Directories for Storing and Building Sources Files

• /usr/src: The main default for storing sources files. According to the FHS, this directory should only be used for reference. Generally, sources should not be built in this directory heirarchy.

[root@linuxmaster ~]# ls -l /usr/src/
drwxr-xr-x. 2 root root 4096 Apr 11  2018 linux-aws-5.3-headers-5.3.0-1035hbash

• /usr/local: For use by the system administrator when installing software locally (based on FHS). /usr/local/src can be used for storing source code.

[root@linuxmaster ~]# ls -l /usr/local/
drwxr-xr-x. 2 root root 4096 Apr 11  2018 bin
drwxr-xr-x. 2 root root 4096 Apr 11  2018 etc
...
drwxr-xr-x. 5 root root 4096 Jul 18 12:47 share
drwxr-xr-x. 2 root root 4096 Apr 11  2018 src

• /opt: Reserved for the installation of add-on application software packages (based on FHS). Files should be placed in a separate /opt/<package> or /opt/<provider> directory tree. <package> is a name that describes the software package, and <provider> is the provider's LANANA (Linux Assigned Names and Numbers Autority).

[root@linuxmaster ~]# ls -l /opt
drwxr-xr-x. 2 root root 4096 Apr 10  2018 websh

Compression Utilities

• gzip: Compresses files using Lempel-Ziv coding (LZYY).gzip on only compress single files but may be used to compress tar archives as well. Compresses files should end in .gz, .z, or .tgz in the case of tar files.

gzip [OPTIONS] [FILENAME(s)]

Option	Description
-k	Keep the original input file (not available in CentOS)
-c	Write output to Standard out
-r	Compress all files in a directory
-1 -> -9	Specify the compression level (default is -6)
-d	Decompress a file
-l	List information about a compressed file
-t	Test the integrity of the compressed file
-v	Increase verbosity

• bzip2 (bunzip2): Compresses files using the Burrows-Wheeler block sorting text compression algorithm and Huffman coding. bzip2 files should end in .bz2, .bz, .tbz2 (tar), or .tbz (tar).

bzip2 [OPTIONS] [FILENAME(s)]

Option	Description
-k	Keep the original input file
-c	Write output to standard out
-r	Compress all files in a directory
-1 -> -9	Specify the compression level (default is -9)
-d	Decompress a file
-z	Force compression regardless of invocation name
-s	Reduce memory usage
-l	List information about a compressed file
-t	Test the integrity of the compressed file
-v	Increase verbosity

• xz (unzx): General-purpose compression tool with a similar command-line syntax to gzip and bzip2. The file extensions for xz is .xz or .txz (tar). The alias unxz can be used for decompression.

xz [OPTIONS] [FILENAME(s)]

Option	Description
-k	Keep the original file (not available in CentOS)
-c	Write output to standard out
-e	Use a slower variant of the compression level
-0 -> -9	Specify the compression level (default is -6)
-d	Decompress a file
-l	List information about a compressed file
-t	Test the integrity of the compressed file
-v	Increase verbosity

• tar: Creates a tar file by converting groups of files and directories into an archive. It was originally used to create archives on magnetic tapes, which is where the name comes from. Tar files end with .tar extension followed by the compression that was used, if any (e.g. .tar.gz).

tar [OPTIONS] [ARCHIVE_NAME] [FILENAME(s)]

Option	Description
-c	Create an archive
-x	Extract an archive
-t	List the content of an archive
-f	Specifgy the archive file name
-v	Show files being processed by the command
-z	Filter the archive through gzip
-j	Filter the archive through bzip2
-J	Filter the archive through xz
-C	Choose a directory to extract the archive to
-A	Append an archive to the end of another archives (does not work with compression)
-d	Find differences between the archive and the file system
--delete	Delete a member from the archive (does not work with compression)
-r	Append a file to the end of an archive
--wildcard	Wildcards match

Install a Program from Source

• configure: This script checks the system to ensure that the project can be built and create the Makefile. Allows for options that can alter the build (see --help to see a list of all the options)

• Makefile: Contain the instructions that are required in order to build the project.

• make: Reads the project specific Makefile and performs all the actions required in order to build (compile) the program.

• make install: Installs the compiled program to a default location or the one specified by the configuration script when using the --prefix option.

Patching a Program from Source

• diff: Compress files line by line. Output displayed can vary based on options passed to the diff command.

diff [OPTION]... FILES

Option	Description
--help	List options and descriptions
-u	Output lines of unified text
-r	Recursively compare any subdirectories found
-N	Treat absent files as empty
-y	Output in two columns

• patch: patch takes a patch file containing a difference listing produced by the diff command and applies those differences to one or more original files, producing patched versions.

patch -pnum <patchfile>
# or
patch [options] [oroginalfile [patchfile]]

Option	Description
--help	List options and descriptions
-d	Change to the directory specified
-b	Create a backup of the original file
-i	Read the patch from the .patch file
-p[#]	Strip slashes from the file path to the file name
-R	Revese the previous patch
-u	Interpret patch file as unified context diff
-n	Interpret patch file as a normal diff
-s	Run the command silently
--dry-run	Print the result of a patch without applying them

206.2 Backup operations (weight: 3)

Candidates should be able to use system tools to back up important system data.

Key Knowledge Areas:

• Knowledge about directories that have to be included in backups

• Awareness of network backup solutions such as Amanda, Bacula, Bareos and BackupPC

• Knowledge of the benefits and drawbacks of tapes, CDR, disk or other backup media

• Perform partial and manual backups.

• Verify the integrity of backup files.

• Partially or fully restore backups.

The following is a partial list of the used files, terms and utilities:

• /bin/sh

• dd

• tar

• /dev/st* and /dev/nst*

• mt

• rsync

Undrestanding Directories to Consider for Backup

Reviewing Directories for Backup

• /home: User home directories. Contains user-specific configuration files and data.

• /etc: System-wide conf files are used to of a program.

• /usr/local: Contains locally installed software. The directory structure is purposefully similar to that of the root directory.

• /opt: Reserved for the installation of add-on application software packages.

• /root: Home directory of the root user. operation Contains configuration files and data for the root user.

• /srv: Data for services provided by the system.

[root@linuxmaster ~]# tree -L 1
.
├── bin -> usr/bin
├── boot
├── dev
├── etc
├── home
├── lib -> usr/lib
├── lib32 -> usr/lib32
├── lib64 -> usr/lib64
├── libx32 -> usr/libx32
├── lost+found
├── media
├── mnt
├── opt
├── proc
├── root
├── run
├── sbin -> usr/sbin
├── srv
├── sys
├── tmp
├── usr
└── var

Reviewing Subdirectories in /var for Backup

• /var/backups (Debian): Contains apt and dpkg package status backups, along with other important system file backups (e.g., /etc/passwd).

• /var/lib: Contains variable state information for applications and the system.

• /var/log: Contains system and application logs.

• /var/mail: Contains local user mail.

• /var/www: A default location for the web root of a web server, which can contain web content.

[root@linuxmaster ~]# tree -L 1 /var
/var/
├── backups
├── cache
├── crash
├── lib
├── local
├── lock -> /run/lock
├── log
├── mail
├── opt
├── run -> /run
├── spool
└── tmp

Comparing Backup Media

Magnetic Tape Storage

• Pros: Cost Efficient, Storage Capacity, Reliability, Security

• Cons: Higher Upfront Cost, Slower Data Access, Susceptibility on Natural Disasters

• The mt Utility: The mt utility is provided bt the mt-st package and is used to control magnetic tape drive operations on a Linux system. Tape devices appear as /dev/st for rewinding tape devices and /dev/nst for non-rewinding tape devices.

Optical Media Storage

• Pros: Compact Physical Size, Low Cost, Read/Write Speed

• Cons: Limited Storage Capacity, Questionable Durability, Variable Speed

Hard Disk Storage

• Pros: Cost Efficient, High Storage Capacity, Reliability, Wide Availability

• Cons: Slower Speed Compared to SSDs, Larger Physical Size, Higher Power Usage, Durability

Comparing Network Backup Solutions

AMANDA

"AMANDA, the Advanced Maryland Automatic Network Disk Archiver, is a backup solution that allows the IT administrator to set up a single primary backup server to back up multiple hosts over network to tape drives/changers or disks or optical media. Amanda uses native utilities and formats (e.g., dump and/or GNU tar) and can back up a large number of servers and workstations running multiple versions of Linux or Unix. Amanda uses a native Windows client to back up Microsoft Windows desktops and servers." (www.amanda.org)

• Developed at the University of Maryland

• Used to back up multiple computers on a network

• Implements a client-server model

• Has a free community edition and a paid enterprise edition

• Has the ability to back up multiple versions of Linux and Unix

• Includes a native Windows client to backup Microsoft Windows desktops and servers

• Supports tape-, disk-, and cloud-based backups

Bacula

"Bacula is a set of computer programs that permits the system administrator to manage backup, recovery, and verification of computer data across a network of computers of different kinds. Bacula can also run entirely upon a single computer and can backup to various types of media, including tape and disk." (www.bacula.org)

• Implements a client-server model

• Supports Linux, Unix, Windows, and macOS

• Bacula Systems provides support contracts for Bacula Enterprise Edition

• Uses various storage media for backups (e.g., tape and disk)

• Has a modular design

• A robust backup solution intended for more advanced users

• Bacula components: Bacula Director, Bacula Console, Bacula File, Bacula Storage, Bacula Catalog, Bacula Monitor

Bareos

"Bareos (Backup Archiving Recovery Open Sourced) is a reliable, cross-network open source software for backup, archiving and recovery of data for all well-established operating systems. Emerged from the Bacula Project in 2010, Bareos was and is actively developed as a fork and enriched with lots of new features." (www.bareos.com)

• Stands for Backup Archiving Recovery Open Sourced (Bareos)

• Is a fork of Bacula that emerged in 2010

• Has an updated web interface as well as other features

• The Bareos project and documentation can be found at www.bareos.org - Professional services are provided at www.bareos.com

• Supports multiple storage media (e.g., disk, tape, and cloud)

• Implements the same core components as Bacula

BackupPC

"BackupPC is a high-performance, enterprise-grade system for backing up Linux, Windows and macOS PCs and laptops to a server's disk. BackupPC is highly configurable and easy to install and maintain." (https://backuppc.github.io/backuppcn/)

• Hosted on GitHub and distributed under the GPL license

• Provides a web interface for initiating/restoring backups and for viewing logs and configurations

• Uses data deduplication (or pooling), so identical files across multiple backups are only stored once

• Uses compression on new files (not already pooled)

• Does not require any client-side software

• The smb protocol is used to extract backup data on Windows clients

• tar over ssh/ rsh/nfs is used to back up data on Linux systems (rsync is also supported)

Creating and Restoring Backups

• rsync: rsync stands for remote sync and is used for copying and synchronizing files and directories, both remotely and locally.

rsync [OPTIONS] SOURCE DESTINATION

Option	Description
-a	Use archive mode which preserves permissions, ownership, etc.
-b	Performs a backup during data synchronization
-e	Specify a protocol
-h	Output in a human-readable format
-n	Performs a dry run
-r	Copy data recursively (do not keep ownership, permissions, etc.)
-u	Skip files that are newer on the destination
-v	Use verbose output
-z	Use compression
--progress	Show transfer progress
--include / --exclude	Choose files/directories to include
--delete	Delete any file or directory not located in the source
--remove-sources-files	Removes source files after a successful transfer

• dd: The dd command is used to vonvert and copy files. This extends to entire disks/partitions, which cane be transferred to and from files or other disks/partitions.

dd [OPERAND]
# or
dd [OPTION]

Option	Description
if	The input file (file/disk/partition)
of	The output file (file/disk/partition)
bs	Read and write BYTES at a time (default: 512)
count	Number of blocks to transfer
ibs	Read up to BYTES at a time (default: 512)
obs	write BYTES at a time (default: 512)
conv	Applies data conversion (use command-seprated list): noerror - dd will continue running even if it encounters error notrunc - dd will not truncate the output file sync - dd will pad input blocks with NULs

# Examples ...

# Copy an HDD to another HDD usin noerror and sync
[root@linuxmaster ~]# dd if=/dev/sda of=/dev/sdb conv=noerror,sync

# Create an image of the HDD
[root@linuxmaster ~]# dd if=/dev/sda of=/home/sda.img

# Restore an image of the HDD
[root@linuxmaster ~]# dd if=/home/sda.img of=/dev/sda

# Create a backup of a CDROM using a block size of 2048
[root@linuxmaster ~]# dd if=/dev/cdrom of=/home/backup.iso bs=2048

# Overwrite a disk write zero using a block size of 4096
[root@linuxmaster ~]# dd if=/dev/zero of=/dev/sda bs=4096

206.3 Notify users on system-related issues (weight: 1)

Candidates should be able to notify the users about current issues related to the system.

Key Knowledge Areas:

• Automate communication with users through logon messages.

• Inform active users of system maintenance

The following is a partial list of the used files, terms and utilities:

• /etc/issue

• /etc/issue.net

• /etc/motd

• wall

• shutdown

• systemctl

Using Automated Messages to Communicate System-Related Issues

• issue: /etc/issue is a text file that contains a message or system identification to be printed before the login prompt. It may contain various @char and \char sequences, if supported by the getty-type program employed on the system.

• issue.net: /etc/issue.net is the historical location for pre-login banners for network logins using protocols lik: telnet or rlogin but can be used for SSH (escaped characters are not processed).

IMPORTANT: To add a message for remote logins, the banner path in /etc/ssh/sshd_config must be updated and the sshd service must be restarted.

Option	Description
\b	Insert the baud rate of the current line.
\d	Insert the current date.
\s	Insert the system name, the name of the operating system.
\l	Insert the name of the current tty line.
\m	Insert the architecture identifier of the machine.
	Insert the node name of the machine, also known as the hostname.
\o	Insert the domain name of the machine.
	Insert the release number of the OS. Insert the current time.
\u	Insert the number of current users logged in.
\U	Insert the string "1 user" or" users", where "users" is the number of current users logged in.
\v	Insert the version of the OS, e.g., the build date, etc.

• /etc/motd: The contents of /etc/motd are displayed after a successful login before the login shell is executed. The abbreviation "motd" stands for "message of the day", and this file has been traditionally used for exactly that (it requires much less disk space than mail to all users).

[root@linuxmaster ~]# cat /etc/motd
Welcome to Ubuntu 18.04.05 LTS (GNU/Linux 5.4.0-1037 x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

 * What are your preferred Linux desktop apps?  Help us set the default
   desktop apps in Ubuntu 18.04 LTS:
   - https://ubu.one/apps1804

10 packages can be updated.
0 updates are security updates.

Last login: Fri Aug 28 18:41:49 2021 from 192.168.0.11

• wall: wall displays a message, the contents of a file, or otherwise its standard input on the terminals of all currently logged-in users.

wall [-n] [-t timeout] [-g group] [message | file]

The /usr/bin/wall command send simple messages to certain system users. Only users who meet the following conditions will receive these messages: Users who are currently into a terminal (tty#) or a terminal-emulator (pts/#), and Users who have their message status set to "yes"

[root@linuxmaster ~]# mesg
is n

[root@linuxmaster ~]# mesg y

[root@linuxmaster ~]# mesg
is y

Option	Description
-n	Suppress the banner (do not print banner, works only for root)
-t	Abandon the write attempt after the time specified (default is 300)
-g	Limit message to members of a group (or GID)
-V	Display version information
-h	Display help text

• shutdown: shutdown is used to halt, power off, or reboot the machine.

  • A shutdown time may be specified in "hh:mm" format or with +m where m is the number of minutes from now (now is an alias for +0)

  • In order to send a wall message, you must specify a time argument.

shutdown [OPTIONS...] [TIME] [WALL...]

Option	Description
-H	Halt the machine
-P	Power off the machine (this is the default)
-r	Reboot the machine
-k	Do not halt, power off, or reboot; just write wall message
-c	Cancel a pending shutdown
--no-wall	Do not send wall message before halt, power-off, reboot.

Commands and Notes

• /usr/src: The main default for storing sources files.

• /usr/local: For use by the system administrator when installing software locally (based on FHS). /usr/local/src can be used for storing source code.

• /opt: Reserved for the installation of add-on application software packages (based on FHS).

• gzip: Compresses files using Lempel-Ziv coding (LZYY).

• bzip2 (bunzip2): Compresses files using the Burrows-Wheeler block sorting text compression algorithm and Huffman coding.

• xz (unzx): General-purpose compression tool with a similar command-line syntax to gzip and bzip2.

• tar: Creates a tar file by converting groups of files and directories into an archive.

• configure: This script checks the system to ensure that the project can be built and create the Makefile.

• Makefile: Contain the instructions that are required in order to build the project.

• make: Reads the project specific Makefile and performs all the actions required in order to build (compile) the program.

• make install: Installs the compiled program to a default location or the one specified by the configuration script when using the --prefix option.

• diff: Compress files line by line. Output displayed can vary based on options passed to the diff command.

• patch: patch takes a patch file containing a difference listing produced by the diff command and applies those differences to one or more original files, producing patched versions.

• rsync: rsync stands for remote sync and is used for copying and synchronizing files and directories, both remotely and locally.

• dd: The dd command is used to vonvert and copy files.

• issue: /etc/issue is a text file that contains a message or system identification to be printed before the login prompt.

• issue.net: /etc/issue.net is the historical location for pre-login banners for network logins using protocols lik: telnet or rlogin but can be used for SSH (escaped characters are not processed).

• /etc/motd: The contents of /etc/motd are displayed after a successful login before the login shell is executed.

• wall: wall displays a message, the contents of a file, or otherwise its standard input on the terminals of all currently logged-in users.

• shutdown: shutdown is used to halt, power off, or reboot the machine.

Sample Questions

1. What are the three steps in installing a program from source? (Choose three.)

• Makefile

• make

• configure

• make install

2. What option of the tar command uses xz compression?

• -j

• -J

• -z

• -c

3. What is the default directory for storing source code (as a reference location)?

• /etc

• /opt

• /usr/local

• /usr/src

4. What network backup solution is a fork of Bacula?

• BackupPC

• Nagios

• Bareos

• AMANDA

5. What command is used to create a patch file?

• make

• patch

• make patch

• diff

6. What option for the rsync command applies compression?

• -z

• -r

• -a

• -u

7. Which directory contains system-wide configuration files?

• /etc

• /srv

• /usr/local

• /home

8. What option for the wall command will limit a message to members of a group?

• -h

• -g

• -n

• -t

9. What file is presented to users who attempt to log in locally?

• /etc/issue

• /etc/ssh/sshd_config

• /etc/motd

• /etc/issue.net

10. Which of the following commands will allow a message to be sent to any tty terminals with write access allowed? (Choose all that apply.)

• mesg

• echo

• mail

• wall

11. To shut down your system without sending a message to users, use which of the following /sbin/shutdown options?

• -c

• -k

• --no-wall

• --wall

• None of the above

12. Your company’s legal department has decided that a login notification is needed on a Linux system that you manage, warning that unauthorized system use is prohibited. Which method is the best one for deploying this legal notification?

• Edit the /etc/issue file, and place the notification there.

• Edit the /etc/motd file, and place the notification there.

• Use the notify-send command to send the notification to users.

• Edit the ∼./bashrc file, and place the notification there.

• None of the above.

13. Assume that money is plentiful, and you want the fastest media to use for your company’s backups. Based on that information, which is the best backup media choice?

• Magnetic tapes

• Optical discs

• HDD

• SSD

• NAS

14. Your co-worker, also a system administrator, hands you an SSD and says, “This has all the files on it that were created and/or modified since the system’s last full backup.” Which of the following backup types can this backup be? (Choose all that apply.)

• Full

• Incremental

• Differential

• None of the above

• All of the above

15. Which of the following Linux directories should be included in a backup when you plan on using the backup data in full system restores? (Choose all that apply.)

• /bin

• /home

• /run

• /tmp

• All of the above

16. Which of the following software packages are GUI and/or web-based backup solutions? (Choose all that apply.)

• Amanda

• Duplicity

• Nagios

• Bacula

• connectd

17. Which of the following tar command options would employ gzip compression for creating a backup tarball? (Choose all that apply.)

• -g

• --gzip

• -z

• -g

• z

18. When using the tar command for an incremental backup, a snapshot file is created. This snapshot file should have which of the following file extensions as part of its name?

• .tar

• .tgz

• .tar.snap

• .snap

• .snar

19. To verify a tar backup immediately after it is created, you use which of the following tar command options? (Choose all that apply.)

• --compare

• --diff

• -d

• -W

• -J

Answer: A, B, C, D. The --compare and --diff (options A and B) are long-style options of -d (option C). These three options compare a tar archive file’s members with external files and list the differences. Option D, the -W option (long style is --verify), automatically verifies a tar archive as soon as it is created. However, it cannot be used with tarballs, only tar archives. Option E, -J, is a tar option that causes the tar command to employ xz compression.

20. Which of the following indicates a tape device that automatically rewinds? (Choose all that apply.)

• /dev/st0

• /dev/nst0

• /dev/ht1

• /dev/nht1

• /dev/nht0

Answer: A, C. The /dev/st0 (SCSI) and /dev/ht1 (PATA) tape device files are for automatically rewinding tape devices. Options B, D, and E all point to non-rewinding tape devices as indicated by the leading n in their device filename, /dev/n*.

21. To control a magnetic tape for backups, use the ...... program.

• tar

• star

• mt

• rsync

• dd

22. Which of the following rsync commands is the proper way to send a backup over the network to the remote host, ServerA, while having the transfer encrypted using OpenSSH?

• rsync -av Project /run/media/ServerA

• rsync -av Project ServerA

• rsync -av ServerA Project

• rsync -av Project ServerA:∼/

• rsync -av Project rsync://ServerA:/

23. Which of the following are true about the dd command? (Choose all that apply.)

• The dd command can be used to create a low-level copy of a hard drive.

• The dd command is popular for daily incremental backups.

• The dd command can be safely used to back up a disk mounted at /.

• The dd command can be used for managing tapes.

• The dd command can be used to zero-out a hard disk.

24. When installing a program from source code, which of the following installation files typically can provide you with additional installation information? (Choose all that apply.)

• README

• INSTALL

• COPYING

• RELEASE-NOTES

• NEWS

25. During the process of installing a program from source, which of the following creates or updates the Makefile with the Makefile.in file’s contents and what it finds on your system?

• INSTALL

• configure

• make

• make install

• cp

26. to build and install a program. However, the installation fails. What could be done to install the program? (Choose two.)

• Install the binaries manually with suinstall

• Run make install with root privileges

• Do not run ./configure in order to maintain the default configuration for correct installation

• Rerun ./configure with a --prefix option where the user has permissions to write

• Run make install_local to install into /usr/local/

27. The following command has just been run successfully: cd /opt; tar xvf /dev/nst0;

What will happen if the command sequence is run again?

• An error saying that there is no tape present is generated because the tape has been ejected after being used

• The contents of /opt will be restored again

• The entire contents of /opt will be replaced with the contents of the next file on the tape

• The contents of /opt will have additional content added from the next file on the tape

28. A system has one hard disk and one CD writer which are both connected to SATA controllers. Which device represents the CD writer?

• /dev/hdb

• /dev/sdd

• /dev/scd1

• /dev/sr0

• /dev/sr1

29. What command ensures that the file systems are written to disk after a lot of write operations? (Specify ONLY the command without any path or parameters.)

Answer: sync

30. Which of the following is a CD-ROM filesystem standard?

• OSI 9660

• ISO 9660

• SR0FS

• ISO 8859

• ROM-EO

31. Which of the following commands restores only those files containing lpi in their name from the archive lpifiles.tar.gz?

• tar xvzf lpifiles.tar.gz --wildcards '*lpi*'

• tar xvzwf lpifiles.tar.gz '*lpi*'

• tar -xvfz lpifiles.tar.gz --deep '*lpi*'

• tar -xvzf lpifiles.tar.gz --subdirs '*lpi*'

• tar xvzf lpifiles.tar.gz --globbing '*lpi*'

32. Which of the following commands erases the contents of the /dev/sdb3 partition?

• rm /dev/sdb3

• dd if=/dev/zero of=/dev/sdb3

• dd of=/dev/zero if=/dev/sdb3

• umount /dev/sdb3

33. Which of the following files will be looked for and used by GNU make, if one of them exists, unless a different file is specified on the command line when trying to compile software from source code? (Choose two.)

• configure

• config.h.in

• makefile

• Makefile

• Makefile.in