Misc
xargs
xargs [-0] [-l<n>] <command>
-0 : Use null character as argument separator (default: newline);
for supporting filenames with blank spaces or newlines;
used in combination with -print0 for find command
-l : (lower-case "L") Pass at most n arguments at a time to the command
- Runs a specified command on files whose
names appear in the
program's input stream
find -type f -name "*.txt" | xargs ls
find -type f -name "*.txt" -print0 | xargs -0 ls
# For each *.txt file containing the text "hello"
find -type f -name "*.txt" | xargs grep -l 'hello' | xargs -l1 ls
-exec, xargs, $(...)
# The following three lines are roughly equivalent:
find -type d -exec ls -adl {} \;
find -type d | xargs ls -adl
ls -adl $(find -type d)
# Note: only the first line can handle directories and filenames containing blankspaces
# The following two lines are equivalent:
find -type d | xargs echo
echo $(find -type d)
-exec calls the second command once for each file
found.xargs and $(...) (command
substitution), call the second
command only once, passing the names of all of the files at once.`...` is another syntax for command substitution,
identical to $(...).
cron
- Time-based job scheduler
- Daemon: crond
- Configuration file: /etc/crontab
min hr dom mon dow command
minute: 0-59
hour: 0-23
day of month: 1-31
month: 1-12, jan, feb, ...
day of week: 0-6, sun, mon, ...
Operators
, : List of values (1,3,4,7,8)
- : Range of values (1-6)
* : Any value
/ : Every nth (*/3)
Shortcuts
@yearly
@annually # Same as @yearly
@monthly
@weekly
@daily
@midnight # Same as @daily
@hourly
@reboot # Run once, at startup
Sorting files
- sort <input-file> [-urnbd]
--output=<output-file>
Options:
- -u : Remove duplicates
- -r : Sort in reverse order
- -n : Numeric sort
- -b : Ingnore leading blanks (doesn't
remove them though)
- -d : Dictionary order (sorts only by
letters and blankspaces)
Comparing files
- diff <file> <file>
- cmp <file> <file>
Symbolic links
- ln -s <existing-file>
<new-link>
Examples
- ln -s /usr/bin/perl /usr/local/bin/perl
App documentation
- <app> --help : Default help;
list of syntax
and command-line arguments
- man <app> : Help manual
- man -k <app> : List of
related help manuals
Processes
- Control-C : Terminates a running
process
- Control-Z : Suspends a running
process and puts it in the
background; to resume the process in the background, type "bg"
- bg: Puts a process in the background
- fg: Puts a process in the foreground
- ps : Shows all processes running on
the current terminal
(tty)
- ps x : Shows all processes running
on a different
terminal or no terminal
- ps -e : Shows all processes
- ps aux : Shows all processes
started by any user, and
which user started them
- pstree : Shows process dependencies
- kill [-<signal>] <pid>
: Send a signal to the
process whose process-id is
<pid>; it's usually good to start with the highest pid when there
are a number of processes that need to be terminated
signal
- 1, sighup : Send the process a
hangup signal, which
the program can optionally act upon
- 15, sigterm : Send the process
a termination signal,
which the program can optionally act upon (default) (same as typing
control-C)
- 9, sigkill : Terminate the
process immediately
Background processes
Command prompt
PS1=”[\[suHhWw]]*[$>]”
s shell
u user
H hostname
h hostname up to the first “.”
w full dir
W cur dir
- Set the PS1 environment variable
PS1=”[\W]$ ” # [cur-dir]$ _
End-of-line characters
- dos2unix <file> : Converts
end-of-line characters
from
DOS to Linux
- unix2dos <file> : Converts
end-of-line characters
from
Linux to DOS
# Identify text files in DOS or Mac format
find -type f -exec grep -Pl $'\r\n' {} \;
# Convert text files from DOS format to Unix format
dos2unix inputfile
tr -d '\r' < inputfile > outputfile
# Convert text files from Mac format to Unix format
tr '\r' '\n' < inputfile > outputfile
# Convert text files from Unix format to DOS format
unix2dos inputfile
tr '\n' '\r\n' < inputfile > outputfile
# Convert text files from Unix format to Mac format
tr '\n' '\r' < inputfile > outputfile
Users
Add
- /usr/sbin/groupadd [-g <gid>] <group> : Add a
group
- /usr/sbin/useradd [-g <group>] [-u <uid>] [-p
password] <user> : Add a user
Update
- /usr/sbin/groupmod [-g <gid>] [-n <new name>]
<group>
- /usr/sbin/usermod [-g <group>] [-u <uid>] [-p
password] <user>
Delete
- /usr/sbin/groupdel <group> : Delete a group
- /usr/sbin/userdel <user> : Delete a user
Password
- passwd : Change the password for
the current user
- passwd <user> : Change the
password for the
specified user
Identify
- whoami : List the current user
- groups : List the groups the
current user belongs to
- w : Displays the currents users of
the system and what
each
one is doing
Misc
- ~/ : Precede a path or
filename with "~/"
to specify a
location relative to the current user's home directory
- ./ : Precede a filename
with "./" to
execute a file located
in the current directory (usually not needed if the current directory
happens to be listed in the system path).
- /sbin/lsmod : Display all modules
currently loaded in
memory
- /sbin/insmod <module> : Loads
a module into memory
- /sbin/rmmod <module> :
Removes a module from memory
- sleep <n>[s,m,h,d] : Pauses
for the specified number of the specified time units (default: seconds)
- usleep <microseconds> :
Pauses for the specified number of microseconds
- logout
- shutdown : Terminates Linux
- halt : Terminates Linux and shuts
the computer down
- reboot : Terminates Linux and
restarts the computer
- lpr <filename> : Sends the
file to the printer
queue
- ldd <filename> : Displays the
libraries needed to
run a
program
- set : Displays all shell variables
- printenv : Displays only the
environment variables
- alias <name>='<value>' :
Defines an abbreviation
alias ls='ls -F'
- unalias <name> : Deletes an
abbreviation
- fsck [-a] <device> :
[Automatically] repair the
file
system
- mke2fs : Creates an ext2 file system
- tune2fs -c <num-mounts>
/dev/hda<n> : Specify
the
number of mounts allowed before the ext2 filesystem on the specified
device is checked again.
- df -h : New total / used /
available space on all mounted
partitions
- du -s[b] <dir> : View
recursize directory size in
KB [or
in bytes]
- free : View memory usage
- uname -r : Find out the version
number of the Linux kernel
- sum <filename> : Calculates
the checksum for a
file
- cksum <filename> : Calculates
the CRC checksum for
a
file
- md5sum <filename> : Generate
the md5 checksum for
the specified file
- touch <filename> : Change the
timestamp of the
specified files to the current date and time
- touch <filename> create file : Create an empty file
in the current directory
- stat -c%y file.txt : Date last
modified
- stat -c%s file.txt : File size
- basename <name>
[<suffix>] : Removes the
directory path and optional filename suffix.
- dirname <name> : Removes the
filename from the full
path.
- cp -dfuvp[r] <source> <dest>
- mv -f <source> <dest>
- mkdir -p <dest>
- rm -fr <dest> # Recursively delete files or
directories
- rmdir <dest> # Only works if the directory is
empty