400 commands for GNU / Linux you should know

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 : interrupts show.
9. cat / proc / meminfo : verify memory usage.
10. cat / proc / swaps : swap files show.
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 -Display USB devices.
16. date : display the system date.
17. cal 2011 : show calendar 2011.
18. Lime July 2011 : show the calendar for the month July 2011.
19. 041217002011.00 date : place (declare, set) date and time.
20. clock-w : save changes to the BIOS date.

Turn off (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 : Logout.

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 : user1 directory go.
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. (If I delete recursive'm saying it with contents).
21. rm-rf dir1 dir2 : delete two folders (directories) with its contents recursively.
22. new_dir dir1 mv : rename or move a file or folder (directory).
23. file1 cp : 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 unison directory.
29. ln-s file1 lnk1 : create a symbolic link to the file or directory.
30. lnk1 file1 ln : 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. file1 file : output (screen dump) the mime type of a text file.
33. iconv-l : lists of known ciphers.
34. iconv-f-t toEncoding fromEncoding 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).

Find 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 '. bin 'in the directory' / home/user1?.
4. find / usr / bin-type f-atime +100 : search binary files not used in the last 100 days.
5. find / usr / bin-type f-mtime -10 : search files created or changed within the last 10 days.
6. find /-name \ *. rpm-exec chmod 755 '{}' \; : search files with '. rpm' and modify permissions.
7. find /-xdev-name \ *. rpm : Search files with '. rpm' extension ignoring removable devices such as cdrom, pen-drive, etc. ....
8. locate \ *. ps : find files with '. ps' executed first with the command 'updatedb'.
9. whereis halt : show location of a binary file, help, or source. In this case asks where the command 'halt'.
10. Which halt : to show the full path (full path) 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. file.iso mount-o loop / 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).

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 nombre_del_grupo : create a new group.
2. groupdel nombre_del_grupo : delete a group.
3. groupmod-n nuevo_nombre_del_grupo viejo_nombre_del_grupo : 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. user1 passwd : change the password of a user (only root).
10. chage-E 2011-12-31 user1 : place a time limit for the user's password. In this case says that the key expires on December 31, 2011.
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 split into 5 columns.
3. chmod ugo + rwx directory1 : ® readable place, write (w) and execute (x) to the owner (u) group (g) and others (o) on the directory 'directory1?.
4. chmod go-rwx directory1 : ® remove read permission, write (w) and (x) running the group (g) and others (o) on the directory 'directory1?.
5. user1 file1 chown : change owner of a file.
6. chown-R user1 directory1 : change the owner of a directory and all files and directories contained within.
7. file1 group1 chgrp : 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 us / 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 gs / 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. ot chmod / home / public : STIKY disable bit in a directory.

Special Attributes on files (Use "+" to place permissions and "-" to remove)

1. chattr + a file1 : enter 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 retrieve the contents of a file even if it is canceled.
8. lsattr : show special attributes.

Archives and 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 to file1.rar TEST_FILE : create a zip file called 'file1.rar'.
7. rar to file1.rar file1 file2 dir1 : compress 'file1?,' file2? and 'dir1? simultaneously.
8. rar x file1.rar : unpack rar file.
9. unrar x file1.rar : unpack 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? y'dir1?.
12. tar-tf archive.tar : display the contents of a file.
13. tar-xvf archive.tar : extract a tarball.
14. archive.tar tar-xvf-C / tmp : extract a tarball in / tmp.
15. archive.tar.bz2 dir1 tar-cvfj : create a tarball compressed into bzip2.
16. tar-xvfj archive.tar.bz2 : decompress a bzip2 compressed tar file
17. archive.tar.gz dir1 tar-cvfz : create a gzipped tarball.
18. tar-xvfz archive.tar.gz : decompress a gzip compressed tar archive.
19. file1.zip zip file1 : create a zipped file.
20. zip-r dir1 file1 file2 file1.zip : compress in zip several files and directories simultaneously.
21. file1.zip unzip : unzip a zip file.

Packages RPM (Red Hat, Fedora and the like)

1. rpm-ivh package.rpm : installing 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" : mostar 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 : mostar the ability given by a rpm package.
14. rpm-q package_name-scripts : scripts show started during installation / removal.
15. rpm-q package_name-changelog : mostar history 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 rpm package integrity.
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 and the like)

1. yum install package_name : download and install a rpm package.
2. package_name.rpm localinstall yum : This will install an RPM and attempt to resolve all dependencies for you, using your repositories.
3. package_name.rpm yum update : update all rpm packages installed on the system.
4. yum update package_name : modernize / 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 : rpm 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 and derivatives)

1. dpkg-i package.deb : install / upgrade a deb package.
2. dpkg-r package_name : remove a deb package system.
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. package_name dpkg-s : to obtain information on a specific package installed on the system.
6. dpkg-L package_name : mostar 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 and derivatives)

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 system.
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 the contents along a.
4. less file1 : commando-like 'more' but can save the file movement and backward movement.
5. -2 file1 head : 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.

Manipulating text

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. Aug grep / 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. Aug grep-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 sample.txt
9. sed '/ ^ $ / d' example.txt : delete all blank lines from the sample.txt
10. sed '/ * # / d, / ^ $ / d' example.txt : Remove comments and blank lines sample.txt
11. echo 'esempio' | tr '[: lower:]' '[: upper:]' : convert lowercase to uppercase.
12. sed-e '1 d '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. fileunix.txt filedos.txt dos2unix : converting a text file format from MSDOS to UNIX.
2. fileunix.txt unix2dos filedos.txt : convert a text file format from UNIX to MSDOS.
3. recode .. HTML  page.html : convert a text file to html.
4. recode-l | more : show all available format conversions.

Analysis of the file system

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. e2fsck-j / dev/hda1 : repair / check integrity ext 3 file system on disk hda1.
6. fsck.ext3 / dev/hda1 : repair / check integrity ext 3 file system on disk hda1.
7. fsck.vfat / dev/hda1 : repair / check integrity of the file system on disk hda1 fat.
8. fsck.msdos / dev/hda1 : repair / check integrity of a file system on disk hda1 two.
9. dosfsck / dev/hda1 : repair / check integrity of a file system on disk hda1 two.

Format a filesystem

1. mkfs / dev/hda1 : create a Linux file system on the partition type hda1.
2. mke2fs / dev/hda1 : create a system file type hda1 Linux ext 2.
3. mke2fs-j / dev/hda1 : create a Linux file system type ext3 (journal) on hda1 partition.
4. mkfs-t vfat 32-F / dev/hda1 : create 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 file system swap.
2. swapon / dev/hda3 : activating a new swap partition.
3. swapon / dev/hda2 / dev/hdb3 : activate two swap partitions.

You save (Backup)

1. dump-0AJ-f / tmp/home0.bak / home : make a complete saves directory '/ home'.
2. dump-1aj-f / tmp/home0.bak / home : make incremental saves directory '/ home'.
3. restore-if / tmp/home0.bak : restoring a saved interactively.
4. rsync-rogpav-delete / home / tmp : synchronization between directories.
5. -rogpav rsync-e ssh-delete / home ip_address :/ tmp : tunnel rsync through SSH .
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 save 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 saves 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 : find and copy 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. gracetime cdrecord-v = 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 "CD Label"-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. cd.iso mount-o loop / 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 : md5sum operating a device such as a CD.

Working with the Network ( 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 255.255.0.0 netmask 192.168.0.0 gw 192.168.1.1 : Configure static route for network search '192 .168.0.0/16?.
10. route of 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 www.example.com : find the host name to resolve the name to an IP address (1).
14. nslookup www.example.com : find the host name to resolve the name to an IP direccióm and vice versa (2).
15. ip link show : mostar the link status of all interfaces.
16. mii-tool eth0 : mostar the link status of 'eth0?.
17. ethtool eth0 : card 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. tcp port 80 tcpdump : show all traffic HTTP .
21. iwlist scan : show wireless networks.
22. iwconfig eth1 : show the configuration of a wireless network card.
23. whois www.example.com : search Whois database.

Microsoft Windows Networking (SAMBA)

1. nbtscan ip_addr : network name resolution changes.
2. nmblookup-A ip_addr : network name resolution changes.
3. smbclient-L ip_addr / hostname : remote actions show a windows host.

IP Tables (FIRE)

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 telnet connections to ent.
7. iptables-t filter-A OUTPUT-p tcp-dport http-j DROP : block connections HTTP to exit.
8. iptables-t filter-A FORWARD-p tcp-dport pop3-j ACCEPT : connections allow POP to a front chain.
9. iptables-t filter-A INPUT-j LOG-log-prefix "DROP INPUT" : recording 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 : diriguidos redirect packets from one host to another.

Monitoring and debugging

1. top : show tasks using most cpu linux.
2. ps-eafw : Linux displays tasks.
3. ps-e-o pid, args-forest : shows Linux tasks in a hierarchical fashion.
4. pstree : show system processes tree.
5. kill -9 ID_Processo : force close and finish process.
6. kill -1 ID_Processo : 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 road 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 : reboot show 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 sconoces 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. file1.gpg gpg : decode a file with GNU Security Guard.
7. wget-r www.example.com : download an entire website.
8. wget-c www.example.com / file.iso : download a file with the possibility to stop the download and resume later.
9. echo 'wget-c www.example.com / files.iso '| at 9:00 : 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. hh alias = 'history' : place an alias for a commando-hh = history.
12. chsh : change the command Shell.
13. chsh-list-shells : it is an appropriate command to find out if you have to remote into another terminal.
14. who-to : 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

Source-

http://www.blackploit.com/2013/05/cheatsheet-comandos-para-GNU-Linux.html#info