linux commands

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chmod, chown

understanding linux file permissions

File permissions are defined by permission group and permission type

  1. permission group
    • owner(u)
    • group(g)
    • all other users(a)
  2. permission type
    • read (r - 4)
    • write(w - 2)
    • execute(x - 1)

permission presentation

The permission in the command line is displayed as _rwxrwxrwx 1 owner:group

  • the first character (underscore _ here) is the special permission flag that can vary.
  • the following three groups of rwx represent permission of owner, group and all other users respectively. If the owner and all users has no read permission, it is __wxrwx_wx
  • follwing that grouping since the integer displays the number of hardlinks to the file
  • the last piece is the owner and group assignment.

special permission flag

The special permission flag can be:

  • _: no special permissions
  • d: directory
  • l: the file or dir is a symbolic link
  • s: This indicated the setuid/setgid permissions. This is not set displayed in the special permission part of the permissions display, but is represented as a s in the read portion of the owner or group permissions.
  • t: This indicates the sticky bit permissions. This is not set displayed in the special permission part of the permissions display, but is represented as a t in the executable portion of the all users permissions

permission modification

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# grant read and write permissions to the user and group
$ chmod ug+rw file1

# remove read and write permissions to the user and group
$ chmod ug-rw file1

# set permission using binary references (owner: rwx = 4+2+1, group: rx = 4+1, all users: rx = 4+1)
$ chmod 755 file1

# change the file permission recursively in the file/dir instead of just the files themselves
$ chmod -R 755 dir1

change owner:group assignments

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# change the owner of file1 to user1 and group to family
$ chown user1:family file1

find

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# find all xml files from the current dir
$ find ./* -name '*.xml'

To find all files modified in the last 24 hours (last full day) in a particular specific directory and its sub-directories:

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$ find /directory_path -mtime -1 -ls

Should be to your liking

The - before 1 is important - it means anything changed one day or less ago. A + before 1 would instead mean anything changed at least one day ago, while having nothing before the 1 would have meant it was changed exacted one day ago, no more, no less.

Another, more humane way:

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find /<directory> -newermt "-24 hours" -ls

or:

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find /<directory> -newermt "1 day ago" -ls

or:

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find /<directory> -newermt "yesterday" -ls

rm

找到文件并删除

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find /home/raven -name abc.txt | xargs rm -rf

# 不使用 xargs

ls

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# list file with creation date and sort by it
$ ls -lct

du

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$ du -sh -- * | sort -hr

List users

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$ cat /etc/passwd | cut -d: -f1

pbcopy

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# copy file content to clipboard
$ pbcopy < test.txt

dstat

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$ dstat -t -a --tcp --output network.log