Following on from a recent post ‘Nmap Cheat Sheet’I have decided to create another cheat sheet but this time for GNU/Linux as I am constantly referring to it for reference. These kind of things are very handy as if you are like myself and don’t use Linux on a daily basis they can play a major part in jogging the little grey cells.
Download: Cheat Sheet commands for GNU/Linux
CheatSheet commands for GNU / Linux
System Information
1. arch: show the architecture of the machine (1).
2. uname -m: show the architecture of the machine (2)..
3. uname -r: show the kernel version used.
4. dmidecode -q: display the components (hardware) system.
5. hdparm -i /dev/hda: show the characteristics of a hard disk.
6. hdparm -tT /dev/sda: make reading test on a hard disk.
7. cat /proc/cpuinfo: CPU information show.
8. cat /proc/interrupts: show interrupts.
9. cat /proc/meminfo: verify memory usage.
10. cat /proc/swaps: show swap files.
11. cat /proc/version: display the version of the kernel.
12. cat /proc/net/dev: network adapters and display statistics.
13. cat /proc/mounts: display the mounted file system.
14. lspci -tv: show PCI devices.
15. lsusb -tv: show USB devices.
16. date: display the system date.
17. cal 2013: show calendar 2013.
18. cal 07 2013: show the calendar for the month July 2013.
19. date 041217002013.00: place (declare, set) date and time.
20. clock -w: save changes to the BIOS date.
Shutdown (Reset System or Log out)
1. shutdown -h now: Shut down system (1).
2. init 0: Shut down system (2).
3. telinit 0: Shut down system (3).
4. halt: shutdown the system (4).
5. shutdown -h hours:minutes &: planned shutdown of the system.
6. shutdown -c: cancel a planned shutdown of the system.
7. shutdown -r now: Restart (1).
8. reboot: Reboot (2).
9. logout: close session.
Files and Directories
1. cd /home: enter the “home” directory.
2. cd ..: go back one level.
3. cd ../..: back 2 levels.
4. cd: go to the root directory.
5. cd ~user1: go to directory user1.
6. cd -: go (back) to the previous directory.
7. pwd: : show the path of the working directory.
8. ls: see the files in a directory.
9. ls -F: see the files in a directory.
10. ls -l: show details of files and folders in a directory.
11. ls -a: show hidden files.
12. ls *[0-9]*: show the files and folders that contain numbers.
13. tree: display files and folders in a tree starting from the root. (1)
14. lstree: display files and folders in a tree starting from the root. (2)
15. mkdir dir1: create a folder or directory called ‘dir1’.
16. mkdir dir1 dir2: create two folders or directories simultaneously (Create two directories at once)
17. mkdir -p /tmp/dir1/dir2: create a directory tree.
18. rm -f file1: delete the file called file1.
19. rmdir dir1: delete the folder called dir1.
20. rm -rf dir1: delete a folder called dir1 with its contents recursively.
21. rm -rf dir1 dir2: delete two folders (directories) with its contents recursively.
22. mv dir1 new_dir: rename or move a file or folder (directory).
23. cp file1: copy a file.
24. cp file1 file2: copy two files together.
25. cp dir /* . : copy all the files in a directory within the current working directory.
26. cp -a /tmp/dir1 . : copy a directory within the current working directory.
27. cp -a dir1: copy a directory.
28. cp -a dir1 dir2: copy two directories.
29. ln -s file1 lnk1: create a symbolic link to the file or directory.
30. ln file1 lnk1: creating a physical link to the file or directory.
31. touch -t 0712250000 file1: modify the real time (time of creation) of a file or directory.
32. file file1: output (screen dump)
33. iconv -l: lists of known encryption.
34. iconv -f fromEncoding -t toEncoding inputFile > outputFile: creates a new form of the input file is encoded in assuming and making a ToEncoding fromEncoding.
35. find . -maxdepth 1 -name *.jpg -print -exec convert ”{}” -resize 80×60 “thumbs/{}” \;: grouping resized files in the current directory and send them to directories in thumbnail view (requires converting from ImageMagick).
Finding Files
1. find / -name file1: file and directory search from the root of the system.
2. find / -user user1: find files and directories belonging to user user1.
3. find /home/user1 -name \*.bin: search files with extension ‘. bin ‘directory within it’ / home/user1.
4. find /usr/bin -type f -atime +100: look at binary files used in the last 100 days.
5. find /usr/bin -type f -mtime -10: find the changed files created within the last 10 days.
6. find / -name \*.rpm -exec chmod 755 ‘{}’ \;: look for files with extension. ‘rpm’ and change permissions.
7. find / -xdev -name \*.rpm: Find files with extension ‘. rpm’ ignoring them removable devices such as cdrom, pen-drive, etc ….
8. locate \*.ps: find files with extension. ‘ps’ primarily executed with the command ‘updatedb’.
9. whereis halt: show the location of a binary file. In this case you are wondering Where he command ‘halt’
10. which halt: show the full path (full path to it) to a binary / executable.
Mounting a file system
1. mount /dev/hda2 /mnt/hda2: mount a disk called hda2. Check first the existence of the directory ‘/ mnt/hda2?, If not, create it.
2. umount /dev/hda2: removing a disk called hda2. Out first from point ‘/ mnt/hda2.
3. fuser -km /mnt/hda2: force umount when the device is busy.
4. umount -n /mnt/hda2: running disassembly without reading the file / etc / mtab. Useful when the file is read-only or the hard drive is full.
5. mount /dev/fd0 /mnt/floppy: mount a floppy disk (floppy).
6. mount /dev/cdrom /mnt/cdrom: mount a cdrom / dvdrom.
7. mount /dev/hdc /mnt/cdrecorder: mount a rewritable cd or dvdrom.
8. mount /dev/hdb /mnt/cdrecorder: mount a rewritable cd / dvdrom (a dvd).
9. mount -o loop file.iso /mnt/cdrom: mount a file or iso image.
10. mount -t vfat /dev/hda5 /mnt/hda5: mount a FAT32 file system.
11. mount /dev/sda1 /mnt/usbdisk: mount a usb thumb drive or a memory (without specifying the filesystem type).
Hard Disk Space
1. df -h: display a list of mounted partitions.
2. ls -lSr |more: show the size of the files and directories sorted by size.
3. du -sh dir1: Estimate the space used by the directory dir1.
4. du -sk * | sort -rn: show the size of the files and directories sorted by size.
5. rpm -q -a –qf ‘%10{SIZE}t%{NAME}n’ | sort -k1,1n: show space used by the installed rpm packages organized by size (Fedora, Redhat and others).
6. dpkg-query -W -f=’${Installed-Size;10}t${Package}n’ | sort -k1,1n: show space used by the packages installed, organized by size (Ubuntu, Debian and others) .
Users and Groups
1. groupadd name_of_the_group: create a new group.
2. groupdel name_of_the_group: delete a group.
3. groupmod -n new_name_of_the_group old_name_of_the_group: rename a group.
4. useradd -c “Name Surname ” -g admin -d /home/user1 -s /bin/bash user1: Create a new user belonging to the “admin”.
5. useradd user1: create a new user.
6. userdel -r user1: delete a user (‘-r’ eliminates home directory).
7. usermod -c “User FTP” -g system -d /ftp/user1 -s /bin/nologin user1: change user attributes.
8. passwd: Changing password.
9. passwd user1: change the password of a user (only root).
10. chage -E 2013-12-31 user1: place a time limit for the user’s password. In this case says that the key expires on December 31, 2013.
11. pwck: correct syntax check the file format of ‘/ etc / passwd’ and the existence of users.
12. grpck: check correct syntax and format of the file ‘/ etc / group’ and the existence of groups.
13. newgrp group_name: Registers a new group to change the default group of newly created files.
File Permissions (Use “+” to place permissions and “-” to remove)
1. ls -lh: Show permissions.
2. ls /tmp | pr -T5 -W$COLUMNS: Terminal divided into 5 columns.
3. chmod ugo+rwx directory1: : enable read permissions (r) , write 
and execute (x) to the owner (u) group (g) and others (o) on the directory ‘directory1
4. chmod go-rwx directory1: remove read permission (r), write and (x) running the group (g) and others (o) on the directory ‘directory1
5. chown user1 file1: cchange owner of a file.
6. chown -R user1 directory1: change the owner of a directory and all files and directories contained within.
7. chgrp group1 file1: changing group of files.
8. chown user1:group1 file1: change user and group ownership of a file.
9. find / -perm -u+s: display all system files with SUID configured.
10. chmod u+s /bin/file1: set the SUID bit on a binary file. The user that running that file takes the same privileges as the owner.
11. chmod u-s /bin/file1: disable SUID bit on a binary file.
12. chmod g+s /home/public: place a SGID bit on a directory-similar to SUID but for directory.
13. chmod g-s /home/public: disable SGID bit on a directory.
14. chmod o+t /home/public: place a bit STIKY in a directory. Allows deletion of files only rightful owners.
15. chmod o-t /home/public: STIKY disable bit in a directory.
Special Attributes on files (Use “+” to place permissions and “-” to remove)
1. chattr +a file1: allows to writte by opening a file only append mode.
2. chattr +c file1: allows a file to be compressed / decompressed automatically.
3. chattr +d file1: ensures that the program ignore delete files during backup.
4. chattr +i file1: convert the file unchanged, so it can not be removed, altered, renamed, or bound.
5. chattr +s file1: allows a file to be deleted safely.
6. chattr +S file1: ensures that a file is modified, the changes are written in synchronous mode as with sync.
7. chattr +u file1: allows you to restore the contents of a file even if it is canceled.
8. lsattr: show special attributes.
Compressed files
1. bunzip2 file1.bz2: decompress in file called ‘file1.bz2.
2. bzip2 file1: compress a file called file1.
3. gunzip file1.gz: decompress a file called ‘file1.gz.
4. gzip file1: compress a file called ‘file1.
5. gzip -9 file1: compress with maximum compression.
6. rar a file1.rar test_file: create a zip file called ‘file1.rar’.
7. rar a file1.rar file1 file2 dir1: compress ‘file1,’ file2 and ‘dir1Simultaneously.
8. rar x file1.rar: decompress rar file.
9. unrar x file1.rar: decompress rar file.
10. tar -cvf archive.tar file1: create an uncompressed tarball.
11. tar -cvf archive.tar file1 file2 dir1: create an archive containing ‘file1,file2 and dir1.
12. tar -tf archive.tar: show contents a file.
13. tar -xvf archive.tar: extract a tarball.
14. tar -xvf archive.tar -C /tmp: extract a tarball in / tmp.
15. tar -cvfj archive.tar.bz2 dir1: create a tarball compressed into bzip2.
16. tar -xvfj archive.tar.bz2: decompress a bzip2 compressed tar file.
17. tar -cvfz archive.tar.gz dir1: create a gzip tarball.
18. tar -xvfz archive.tar.gz: decompress a gzip compressed tar archive.
19. zip file1.zip file1: create a zip file.
20. zip -r file1.zip file1 file2 dir1: compress in zip several files and directories simultaneously.
21. unzip file1.zip: decompress a zip file.
RPM Packages (Red Hat, Fedora…etc)
1. rpm -ivh package.rpm: install an rpm package.
2. rpm -ivh –nodeeps package.rpm: installing an rpm package ignoring dependencies requests.
3. rpm -U package.rpm: upgrade a rpm package without changing configuration files.
4. rpm -F package.rpm: upgrade a rpm package only if it is installed.
5. rpm -e package_name.rpm: remove a rpm package.
6. rpm -qa: show all rpm packages installed on the system.
7. rpm -qa | grep httpd: show all rpm packages with the name “httpd”.
8. rpm -qi package_name: get information on a specific package installed.
9. rpm -qg “System Environment/Daemons”: show rpm packages of a software group.
10. rpm -ql package_name: show list of files given by a rpm package installed.
11. rpm -qc package_name: show configuration files list given by a rpm package installed.
12. rpm -q package_name –whatrequires: show list of dependencies required for a rpm package.
13. rpm -q package_name –whatprovides: show the capacity provided by a rpm package.
14. rpm -q package_name –scripts: scripts show started during installation / removal.
15. rpm -q package_name –changelog: display the history of revisions of a rpm package.
16. rpm -qf /etc/httpd/conf/httpd.conf: check which rpm package belongs to a given file.
17. rpm -qp package.rpm -l: show list of files given by a rpm package not yet been installed.
18. rpm –import /media/cdrom/RPM-GPG-KEY: Import digital signature public key.
19. rpm –checksig package.rpm: verify the integrity of a package rpm.
20. rpm -qa gpg-pubkey: verify the integrity of all rpm packages installed.
21. rpm -V package_name: check the file size, licenses, rates, owner, group, check MD5 digest and last modified.
22. rpm -Va: check all rpm packages installed on the system. Use with caution.
23. rpm -Vp package.rpm: verify a rpm package not yet installed.
24. rpm2cpio package.rpm | cpio –extract –make-directories *bin*: extracting executable file from a rpm package.
25. rpm -ivh /usr/src/redhat/RPMS/`arch`/package.rpm: install a package built from a source rpm.
26. rpmbuild –rebuild package_name.src.rpm: build a rpm package from a source rpm.
YUM packages updater (Red Hat, Fedora…etc)
1. yum install package_name: download and install a rpm package..
2. yum localinstall package_name.rpm: This will install an RPM and attempt to resolve all dependencies for you, using your repositories.
3. yum update package_name.rpm: update all rpm packages installed on the system.
4. yum update package_name: upgrade a rpm package.
5. yum remove package_name: remove a rpm package.
6. yum list: list all packages installed on the system.
7. yum search package_name: Find a package repository rpm.
8. yum clean packages: clean a cache erasing downloaded packages.
9. yum clean headers: remove all header files that the system uses to resolve the dependency.
10. yum clean all: delete from the cache packages and header files.
Deb packages (Debian, Ubuntu…etc)
1. dpkg -i package.deb: upgrade a deb package.
2. dpkg -r package_name: remove a deb package.
3. dpkg -l: show all deb packages installed on the system.
4. dpkg -l | grep httpd: show all deb packages with the name “httpd”
5. dpkg -s package_name: to obtain information on a specific package installed on the system.
6. dpkg -L package_name: show list of files given by a package installed on the system.
7. dpkg –contents package.deb: show list of files given by a package not yet installed.
8. dpkg -S /bin/ping: check which package owns a given file.
APT packages updater (Debian, Ubuntu …etc)
1. apt-get install package_name: install / upgrade a deb package.
2. apt-cdrom install package_name: install / upgrade a deb package from cdrom.
3. apt-get update: update the package list.
4. apt-get upgrade: update all installed packages
5. apt-get remove package_name: remove a deb package.
6. apt-get check: check the correct resolution of dependencies.
7. apt-get clean: clean up cache from packages downloaded.
8. apt-cache search searched-package: returns list of packages that corresponds to the series’ wanted packages. ”
View the contents of a file
1. cat file1: view the contents of a file starting from the first row.
2. tac file1: view the contents of a file starting from the last line.
3. more file1: view content along a file.
4. less file1: command like ‘more’ but can save the file movement and backward movement.
5. head -2 file1: see the first two lines of a file.
6. tail -2 file1: see the last two lines of a file.
7. tail -f /var/log/messages: see in real time what has been added to the file.
Text Manipulation
1. cat file1 file2 .. | command <> file1_in.txt_or_file1_out.txt: general syntax for text manipulation using PIPE, STDIN and STDOUT.
2. cat file1 | command( sed, grep, awk, grep, etc…) > result.txt: general syntax to manipulate a text from a file and write the output to a new file.
3. cat file1 | command( sed, grep, awk, grep, etc…) » result.txt: general syntax to manipulate a text from a file and add result in an existing file.
4. grep Aug /var/log/messages: search words “Aug” on file ‘/ var / log / messages’.
5. grep ^Aug /var/log/messages: look for words that begin with “Aug” on file ‘/ var / log / messages’
6. grep [0-9] /var/log/messages: select all lines in the file ‘/ var / log / messages’ that contain numbers.
7. grep Aug -R /var/log/*: search for the string “Aug” in directory ‘/ var / log’ and below.
8. sed ‘s/stringa1/stringa2/g’ example.txt: relocate “string1” with “string2” in example.txt
9. sed ‘/^$/d’ example.txt: delete all blank lines from the example.txt
10. sed ‘/ *#/d; /^$/d’ example.txt: Remove comments and blank lines example.txt
11. echo ‘esempio’ | tr ‘[:lower:]‘ ‘[:upper:]‘: convert lowercase to uppercase
12. sed -e ’1d’ result.txt: deletes the first line of the file sample.txt
13. sed -n ‘/stringa1/p’: display only lines that contain the word “string1”.
Character set and file conversion
1. dos2unix filedos.txt fileunix.txt: convert a text file format from MSDOS to UNIX.
2. unix2dos fileunix.txt filedos.txt: convert a text file format from UNIX to MSDOS.
3. recode ..HTML < page.txt > page.html: convert a text file to html.
4. recode -l | more: show all available format conversions.
Analysis of the file systems
1. badblocks -v /dev/hda1: Check for bad blocks on disk hda1.
2. fsck /dev/hda1: repair / check integrity Linux system file on disk hda1.
3. fsck.ext2 /dev/hda1: repair / check integrity ext 2 file system on disk hda1.
4. e2fsck /dev/hda1: repair / check integrity ext 2 file system on disk hda1.
5. fsck.ext3 /dev/hda1: repair / check integrity ext 3 file system on disk hda1.
6. fsck.vfat /dev/hda1: repair / check integrity ext 3 file system on disk hda1.
7. fsck.msdos /dev/hda1: repair / check integrity of a file from MSDOS system on disk hda1.
8. dosfsck /dev/hda1: repair / check integrity of a file from a DOS system on disk hda1.
Formatting a filesystem
1. mkfs /dev/hda1: create a Linux file system on the partition hda1.
2. mke2fs /dev/hda1: create a system file type on the partition hda1
3. mke2fs -j /dev/hda1: create a Linux file system type ext3 (journal) on hda1 partition.
4. mkfs -t vfat 32 -F /dev/hda1: ccreate a FAT32 file system on hda1.
5. fdformat -n /dev/fd0: flooply format a disk.
6. mkswap /dev/hda3: create a swap file system.
Working with SWAP
1. mkswap /dev/hda3: create a swap file system.
2. swapon /dev/hda3: activate a new swap partition.
3. swapon /dev/hda2 /dev/hdb3: activate two swap partitions.
Backup
1. dump -0aj -f /tmp/home0.bak /home: make a complete backup directory ‘/ home’.
2. dump -1aj -f /tmp/home0.bak /home: make incremental backup directory ‘/ home’.
3. restore -if /tmp/home0.bak: restoring a backup interactively.
4. rsync -rogpav –delete /home /tmp: synchronization between directories.
5. rsync -rogpav -e ssh –delete /home ip_address:/tmp: rsync through SSH tunnel.
6. rsync -az -e ssh –delete ip_addr:/home/public /home/local: synchronize a local directory with a remote directory via ssh and compression.
7. rsync -az -e ssh –delete /home/local ip_addr:/home/public: Synchronize a remote directory with a local directory via ssh and compression.
8. dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr ‘dd of=hda.gz’: make a backup on a hard disk on a remote host via ssh.
9. dd if=/dev/sda of=/tmp/file1: save the contents of a hard drive to a file. (In this case the hard drive is “sda” and the file “file1”).
10. tar -Puf backup.tar /home/user: make incremental backup directory ‘/ home / user’.
11. ( cd /tmp/local/ && tar c . ) | ssh -C user@ip_addr ‘cd /home/share/ && tar x -p’: copy the contents of a directory on a remote directory via ssh.
12. ( tar c /home ) | ssh -C user@ip_addr ‘cd /home/backup-home && tar x -p’: copy a local directory on a remote directory via ssh.
13. tar cf – . | (cd /tmp/backup ; tar xf – ): local copy preserving permits and links from one directory to another.
14. find /home/user1 -name ‘*.txt’ | xargs cp -av –target-directory=/home/backup/ –parents: finding and copying all files with ‘. txt’ from one directory to another.
15. find /var/log -name ‘*.log’ | tar cv –files-from=- | bzip2 > log.tar.bz2: find all files with ‘. log’ and make a bzip file.
16. dd if=/dev/hda of=/dev/fd0 bs=512 count=1: make a copy of MRB (Master Boot Record) to floppy.
17. dd if=/dev/fd0 of=/dev/hda bs=512 count=1: restore the backup of the MBR (Master Boot Record) saved on a floppy.
CD-ROM
1. cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force: clean or erase a rewritable cd.
2. mkisofs /dev/cdrom > cd.iso: create an iso image of cdrom on disk.
3. mkisofs /dev/cdrom | gzip > cd_iso.gz: create a compressed iso image of cdrom on disk.
4. mkisofs -J -allow-leading-dots -R -V “Label CD” -iso-level 4 -o ./cd.iso data_cd: create an iso image from a directory.
5. cdrecord -v dev=/dev/cdrom cd.iso: burn an iso image.
6. gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom -: burn an iso image compression.
7. mount -o loop cd.iso /mnt/iso: mount an iso image.
8. cd-paranoia -B: take songs from a cd to wav files.
9. cd-paranoia – ”-3”: take the first 3 songs from a CD to wav files.
10. cdrecord –scanbus: scan bus to identify the channel scsi.
11. dd if=/dev/hdc | md5sum: to run an md5sum in a device such as a cd.
LAN and Wi-Fi
1. ifconfig eth0: show the configuration of an Ethernet network card.
2. ifup eth0: activate an interface ‘eth0’
3. ifdown eth0: disable an interface ‘eth0’
4. ifconfig eth0 192.168.1.1 netmask 255.255.255.0: set an IP address.
5. ifconfig eth0 promisc: configure ‘eth0’ common mode for packets (sniffing).
6. dhclient eth0: active interface ‘eth0’ dhcp mode.
7. route -n: show route table
8. route add -net 0/0 gw IP_Gateway: default input configuration.
9. route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1: Configure static route for network search ‘192 .168.0.0/16’
10. route del 0/0 gw IP_gateway: remove the static route.
11. echo “1” > /proc/sys/net/ipv4/ip_forward: enable ip route.
12. hostname: display the system hostname.
13. host http://www.example.com: hostname search to resolve the name to an IP address (1).
14. nslookup http://www.example.com: find the host name to resolve the name to an IP address and vice versa (2)
15. ip link show: show the link status of all interfaces.
16. mii-tool eth0: show the link status of ‘eth0’
17. ethtool eth0: display statistics for ‘eth0’.
18. netstat -tup: show all active network connections and their PID.
19. netstat -tupl: show all network services listening on the system and its PID.
20. tcpdump tcp port 80: show all HTTP traffic.
21. iwlist scan: show wireless networks.
22. iwconfig eth1: show the configuration of a wireless network card.
23. whois http://www.example.com: search Whois database.
Microsoft Windows Networks (SAMBA)
1. nbtscan ip_addr: net bios name resolution.
2. nmblookup -A ip_addr: net bios name resolution.
3. smbclient -L ip_addr/hostname: show remote actions of a windows host.
IP Tables (FIREWALL)
1. iptables -t filter -L: show all chains of the filter table.
2. iptables -t nat -L: show all chains of the nat table.
3. iptables -t filter -F: clear all rules from the filter table.
4. iptables -t nat -F: clean all nat table rules.
5. iptables -t filter -X: delete any user-created chain.
6. iptables -t filter -A INPUT -p tcp –dport telnet -j ACCEPT: allow input telnet connections.
7. iptables -t filter -A OUTPUT -p tcp –dport http -j DROP: block output HTTP connections.
8. iptables -t filter -A FORWARD -p tcp –dport pop3 -j ACCEPT: allow POP connections to a front chain.
9. iptables -t filter -A INPUT -j LOG –log-prefix “DROP INPUT”: registering an input string.
10. iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE: configure a PAT (Port Address Translation) on eth0, hiding the forced departure packages.
11. iptables -t nat -A PREROUTING -d 192.168.0.1 -p tcp -m tcp –dport 22 -j DNAT –to-destination 10.0.0.2:22: redirect packets directed from one host to another.
Monitoring and debugging
1. top: show cpu processes.
2. ps -eafw: show cpu processes.
3. ps -e -o pid,args –forest: shows Linux processes in a hierarchal manner.
4. pstree: show system processes tree.
5. kill -9 ID_Process: force close and finish process..
6. kill -1 ID_Process: force a process to reload the configuration.
7. lsof -p $$: display a list of files opened by processes.
8. lsof /home/user1: lists open files on a given path by the system.
9. strace -c ls >/dev/null: show system calls made and received by a process.
10. strace -f -e open ls >/dev/null: display library calls.
11. watch -n1 ‘cat /proc/interrupts’: show interruptions in real time.
12. last reboot: show reboot history.
13. lsmod: display the loaded kernel.
14. free -m: Displays the status of RAM in megabytes.
15. smartctl -A /dev/hda: monitor the reliability of a hard drive via SMART.
16. smartctl -i /dev/hda: check if SMART is enabled on a hard disk.
17. tail /var/log/dmesg: show events inherent in the charging process of the kernel.
18. tail /var/log/messages: show system events.
Other useful commands
1. apropos …keyword: display a list of commands that belong to the keywords of a program, are useful when you know what makes your program, but not know the command name.
2. man ping: display manual pages on-line, for example, in a ping command, use the ‘-k’ to find any related command.
3. whatis …keyword: Displays the description of what the program does.
4. mkbootdisk –device /dev/fd0 `uname -r`: create a floppy boteable.
5. gpg -c file1: encrypt a file with GNU security guard.
6. gpg file1.gpg: decode a file with GNU Security Guard.
7. wget -r http://www.example.com: download an entire website.
8. wget -c http://www.example.com/file.iso: download a file with the possibility to stop the download and resume later.
9. echo ‘wget -c http://www.example.com/files.iso‘ | at 09:00: Start a download at any time. In this case begin at 9 am.
10. ldd /usr/bin/ssh: display the shared libraries required by ssh.
11. alias hh=’history’: place an alias for a command-hh = history.
12. chsh: change the command Shell.
13. chsh –list-shells: is an appropriate command to find out if you have to remote into another terminal.
14. who -a: show who is registered, and print time of last import system, dead processes, system logging processes, active processes produced by init, current and past performance of the system clock changes.
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