Schedule a queue to run at 9am on March 1st. Note: Ctrl-d to save and exit.$ at 9am March 1
- Schedule a queue to run after 5 minutes.
$ at now +5 minutes
- Check any jobs pending to run, same as at -l .
$ atq
- Empty out a file.
$ cat /dev/null > /path/to/file
- Change directory, see also pushd and popd.
$ cd
- List run level information for the service type.
chkconfig --list
- Change owner recursively.
$ chown -R : /path/to/directory
- Change shell.
$ chsh
- Scan recursively for viruses.
clamscan -r
- Compare two files.
cmp file1 file2
- Copy keeping the directory structure.
$ cp --parent /source/path /destination/path
- Copy keeping the permissions of the user.
$ cp -p
- Copy recursive.
$ cp -r
- Copy without shell aliasing.
$ \cp
- List crontab for user.
$ crontab -u -l
- Check current date and time.
$ date
- Set current date and time, may need to set the hardware clock to the system time too, `man hwclock`.
$ date -s 'Wed May 28 11:35:00 EST 2003'
- Show disk free in human readable format.
$ df -h
- Configure interface using DHCP protocol.
$ dhclient eth0
- Find context differences between two files.
$ diff -c
- Creating a patch file.
$ diff -Naur oldDir/oldFile newDir/newFile > new_patchFile
- Kernel buffer
$ dmesg
- Show disk used in human readable format.
$ du -h /path/to/directory
- Find files larger than 10MB.
$ find /path/to/file -size +10000k
- Find file permissions with setuids.
find / \( -perm -4000 -o -perm -2000 \) -exec ls -ldb {} \;>> /tmp/suids
- Search for world writable files and directories.
$ find / -perm -002
- Display information on free and used memory.
$ free
- Grep on word boundaries.
grep -w
- Count the number of mathces - similar to “wc -l”.
$ grep -c
- Perform timings of device reads for benchmark and comparison purposes.
$ hdparm -t /dev/hda1
- Set the hardware clock to the current system time.
$ hwclock --systohc
- Configure network interface.
$ ifconfig
- Add an additional ip to eth0.
$ ifconfig eth0 
xxx.xxx.xxx.xxx
- Install loadable kernel module. You can also use `modprobe` to do the same.
$ insmod
- Displays information about your system’s CPU and I/O.
$ iostat [ interval [ count ] ]
- List iptables firewall rules in numeric format.
$ iptables -L -n
- HangUP process so it will re-read the config file.
$ killall -HUP
- Install the boot loader and increase verborsity.
$ lilo -v -v
- Query the boot map.
$ lilo -q
- One time boot to the named kernel.
$ lilo -R
- Create symbolic link to the target file or directory.
$ ln -s
- Configure dynamic linker run-time bindings
$ ldconfig
- List the IPs bound via Ensim
$ listaliases
- Quickly search for indexed files. Run `updatedb` to update the indexed database.
$ locate
- List files.
$ ls
- List loaded kernel modules
$ lsmod
- Create the access.db file database map for sendmail.
$ makemap hash /etc/mail/access.db < /etc/mail/access
- Create/Make a new directory.
$ mkdir
- Generate a random 128 character length password.
$ mkpasswd -l 128
- Read in the contents of your mbox (or the specified file).
$ mail -f /var/mail/nameOfFile
- Print the mail queue
$ mailq
$ mailstat /path/to/procmail/log
- Description of the hierarchy directory structure of the system
$ man hier
- Check the MD5 message digest.
$ md5sum
- Mount points check.
$ mount
- Provide information about your systems’ processor.
$ mpstat [ interval [ count ] ]
$ ncftpget -R -u -p
hostname /local_dir /remote_dir
$ netstat -a | grep -i listen
- Will show you who is attached to what port.
$ netstat -anpe
$ netstat -n
- See which programs are listening on which port
$ netstat -lnp
- Will show you what local TCP ports are open and what programs are running on them.
$ netstat -lntpe
- Will show you what local UDP ports are open and what programs are running on them.
$ netstat -lnupe
- Run a program with modified scheduling priority. (# range between -20 to +20, negative is higher prio
rity)$ nice -n # [command to nice]
- Scan network
$ nmap -v hostname/ip
- Patch and keep a backup
$ patch -p# -b < patch_file
$ ps -ecaux
- Turn off all quotas for users and groups, verbose mode
$ quotaoff -augv
- Check quota for all users and groups interactively, do quotaoff first.
$ quotacheck -augmiv
- Turn on all quotas for users and groups
$ quotaon -augv
- Add host ip to route on a particular device.
$ route add -host xxx.xxx.xxx.xxx dev eth0
$ rdate
$ rm
- Remove kernel module
$ rmmod
- Display the routing table in numeric.
$ route -n
$ rpm
- Uninstall/erase package.
$ rpm -e
- Erase without dependency check.
$ rpm -e --nodeps
- List out installed rpms by date, latest on top.
$ rpm -qa --last | less
- Rebuild rpm database.
$ rpm --rebuilddb
- Find which package owns the file.
$ rpm -qf /path/to/file
$ rpm -q --whatprovides /path/to/file
- Verify package.
$ rpm -V
or
$ rpm -Vf /path/to/file
- Locate documentation for the package that owns the file.
$ rpm -qdf /path/to/file
- Query information on package.
$ rpm -qip
- Query files installed by package.
$ rpm -qlp
- Gives list of files that will be installed/overwritten.
$ rpm -ql
- Will show the scripts that will be executed.
$ rpm -q --scripts
- Display system activity information
$ sar
- Print a 0 padded sequence of numbers.
$ seq -w 1 10
- Record eveything printed on your terminal screen.
$ script -a
Ctrl+D to exit out. `more ` to view.
- Check the status of a service.
$ service status
- Restart after shutdown and force fsck (fsck may take a while).
$ shutdown -rF now
- Split a file into pieces with numeric suffixes, so it can be burnt to cds.
$ split -d -b 640k big_input_filename.gz piece_file_prefix.gz.
To piece it back you can `cat piece_file_prefix.gz.* > original.gz`
- Determine if a network service binary is linked againt tcp wrapper, libwrap.a
$ strings -f | grep hosts_access
$ tar
$ tar -cvzf fileName.tar.gz `find /file/path -mtime -1 ! -type d -print`
$ tar -xvzpf fileName.tar.gz /path/to/file.txt
$ tcpdump -i eth0 dst port 80 | more
$ top
- View the full command line.
$ top -c
$ touch
- Similar to `which` - shows full path to the command.
$ type
$ ulimit -a
$ uname
- Update package profile with rhn
$ up2date -p
- Install package via up2date.
$ up2date -i
$ uptime
$ usermod
- Utility reports virtual memory statistics
$ vmstat [second interval] [no. of count]
- Show who is logged on and what they are doing.
$ w
- Periodically watch output of a command in full screen
$ watch ''
$ webalizer -c /path/to/webalizer.conf
- Recursive download of a url, converting links, no parent.
$ wget -r -k -np
- Mirror, convert links, backup original, dynamic to html and output a “logFile”.
$ wget -m -k -K -E -o [logFile]
- Locate the binary, source, and manual page files for a command.
$ whereis
- Shows the full path of command.
$ which
- Show who is logged on.
$ who
- Yum package updates
$ yum check-update -- check to see what updates are needed
$ yum info -- show basic information about a package
$ yum update -- update particular package
- Control jobs:
$ Ctrl-z -- suspend foreground job
$ jobs -- list jobs
$ bg -- send job to background
$ fg -- bring job to foreground
