1. Schedule a queue to run at 9am on March 1st. Note:
Ctrl-d to save and exit.
# at 9am March 1
2. Schedule a queue to run after 5 minutes.
# at now +5 minutes
3. Check any jobs pending to run, same as at -l .
# atq
4. Empty out a file.
# cat /dev/null > /path/to/file
5. Change directory, see also pushd and popd.
# cd
6. List run level information for the service type.
# chkconfig --list
7. Change owner recursively.
# chown -R : /path/to/directory
8. Change shell.
# chsh
9. Scan recursively for viruses.
# clamscan -r
10. Compare two files.
# cmp file1 file2
11. Copy keeping the directory structure.
# cp --parent /source/path /destination/path
12. Copy keeping the permissions of the user.
# cp -p
13. Copy recursive.
# cp -r
14. Copy without shell aliasing.
# \cp
15. List crontab for user.
# crontab -u -l
16. Check current date and time.
# date
17. 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'
18. Show disk free in human readable format.
# df -h
19. Configure interface using DHCP protocol.
# dhclient eth0
20. Find context differences between two files.
# diff -c
21. Creating a patch file.
# diff -Naur oldDir/oldFile newDir/newFile > new_patchFile
22. Kernel buffer
# dmesg
23. Show disk used in human readable format.
# du -h /path/to/directory
24. Find files larger than 10MB.
# find /path/to/file -size +10000k
25. Find file permissions with setuids.
find / \( -perm -4000 -o -perm -2000 \) -exec ls -ldb {} \;>> /tmp/suids
26. Search for world writable files and directories.
# find / -perm -002
27. Display information on free and used memory.
# free
28. Grep on word boundaries.
grep -w
29. Count the number of mathces - similar to “wc -l”.
# grep -c
30. Perform timings of device reads for benchmark and comparison purposes.
# hdparm -t /dev/hda1
31. Set the hardware clock to the current system time.
# hwclock --systohc
32. check the ip address
# ifconfig
33. Add an ip address to eth0.
# ifconfig eth0:x xxx.xxx.xxx.xxx
34. Install loadable kernel module. You can also use `modprobe` to do the same.
# insmod
35. Displays information about your system’s
CPU and I/O.
# iostat [ interval [ count ] ]
36. List iptables
firewall rules in numeric format.
# iptables -L -n
37. HangUP process so it will re-read the config file.
# killall -HUP
38. Install the boot loader and increase verborsity.
# lilo -v -v
39. Query the boot map.
# lilo -q
40. One time boot to the named kernel.
# lilo -R
41. Create symbolic link to the target file or directory.
# ln -s
42. Configure dynamic linker run-time bindings
# ldconfig
43. List the IPs bound via Ensim
# listaliases
44. Quickly search for indexed files. Run `updatedb` to update the indexed
database.
# locate
45. List files.
# ls
46. List loaded kernel modules
# lsmod
47. Create the access.db file database map for sendmail.
# makemap hash /etc/mail/access.db < /etc/mail/access
48. Create/Make a new directory.
# mkdir
49. Generate a random 128 character length password.
# mkpasswd -l 128
50. Read in the contents of your mbox (or the specified file).
# mail -f /var/mail/nameOfFile
51. Print the mail queue
# mailq
52.
# mailstat /path/to/procmail/log
53. Description of the hierarchy directory structure of the system
# man hier
54. Check the MD5 message digest.
# md5sum
55. Mount points check.
# mount
56. Provide information about your systems’ processor.
# mpstat [ interval [ count ] ]
57.
# ncftpget -R -u -p
hostname /local_dir /remote_dir
58.
# netstat -a | grep -i listen
59. Will show you who is attached to what port.
# netstat -anpe
60.
# netstat -n
61. See which programs are listening on which port
# netstat -lnp
62. Will show you what local TCP ports are open and what programs are running on them.
# netstat -lntpe
63. Will show you what local UDP ports are open and what programs are running on them.
# netstat -lnupe
64. Run a program with modified scheduling priority. (# range between -20 to +20, negative is higher priority)
# nice -n # [command to nice]
65. Scan network
# nmap -v hostname/ip
66. Patch and keep a backup
# patch -p# -b < patch_file
67.
# ps -ecaux
68. Turn off all quotas for users and groups, verbose mode
# quotaoff -augv
69. Check quota for all users and groups interactively, do quotaoff first.
# quotacheck -augmiv
70. Turn on all quotas for users and groups
# quotaon -augv
71. Add host ip to route on a particular device.
# route add -host xxx.xxx.xxx.xxx dev eth0:x
72.
# rdate
73. Remove file
# rm
74. Remove kernel module
# rmmod
75. Display the routing table in numeric.
# route -n
76.
# rpm
77. Uninstall/erase package.
# rpm -e
78. Erase without dependency check.
# rpm -e --nodeps
79. List out installed rpms by date, latest on top.
# rpm -qa --last | less
80. Rebuild rpm database.
# rpm --rebuilddb
81. Find which package owns the file.
# rpm -qf /path/to/file
# rpm -q --whatprovides /path/to/file
82. Verify package.
# rpm -V
or
# rpm -Vf /path/to/file
83. Locate documentation for the package that owns the file.
# rpm -qdf /path/to/file
84. Query information on package.
# rpm -qip
85. Query files installed by package.
# rpm -qlp
86. Gives list of files that will be installed/overwritten.
# rpm -ql
87. Will show the scripts that will be executed.
# rpm -q --scripts
88. Display system activity information
# sar
89. Print a 0 padded sequence of numbers.
# seq -w 1 10
90. Record eveything printed on your terminal screen.
# script -a
Ctrl+D to exit out. `more ` to view.
91. Check the status of a service.
# service status
92. Restart after shutdown and force fsck (fsck may take a while).
# shutdown -rF now
93. 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`
94. Determine if a network service binary is linked againt tcp wrapper, libwrap.a
# strings -f | grep hosts_access
96. how to use tar
# tar -cvzf fileName.tar.gz `find /file/path -mtime -1 ! -type d -print`
97.
# tar -xvzpf fileName.tar.gz /path/to/file.txt
98. How to use tcpdump
# tcpdump -i eth0 dst port 80 | more
99. System process status
# top
100. View the full command line.
# top -c
101. Create empty file of 0 byte
# touch
102. Similar to `which` - shows full path to the command.
# type
103. Check the limit of user
# ulimit -a
104. Check the version of kernel running
# uname -a
105. Update package profile with rhn
# up2date -p
106. Install package via up2date.
# up2date -i
107.
# uptime
108.
# usermod
109. Utility reports virtual memory statistics
# vmstat [second interval] [no. of count]
110. Show who is logged on and what they are doing.
# w
111. Periodically watch output of a command in full screen
# watch ''
112. Run and generate the apache reports using webalizer
# webalizer -c /path/to/webalizer.conf
113. Recursive download of a url, converting links, no parent.
# wget -r -k -np
114. Mirror, convert links, backup original, dynamic to html and output a “logFile”.
# wget -m -k -K -E -o [logFile]
115. Locate the binary, source, and manual page files for a command.
# whereis
116. Shows the full path of command.
# which
117. Show who is logged on.
# who
118. 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
119. Control jobs:
# Ctrl-z -- suspend foreground job
# jobs -- list jobs
# bg -- send job to background
# fg -- bring job to foreground
