od:dump files in octal and other formats(以八进制或其他格式转储文件;dump:倾倒,倾销)
-t(--format=TYPE):select output format or formats
TYPE is made up of one or more of these specifications:
a:named character,ignoring high-order bit 默认字符串
c:ASCII character or backslash escape(backslash:反斜杠) ASCII码
d[SIZE]:signed decimal,SIZE bytes per integer 有符号整型,每个整数占SIZE bytes
f[SIZE]:floating point,SIZE bytes per integer 浮点数,每个数占SIZE bytes
o[SIZE]:octal,SIZE bytes per integer 八进制,每个数占SIZE bytes
u[SIZE]:unsigned decimal,SIZE bytes per integer 无符号整型,每个整数占用SIZE bytes
x[SIZE]:hexadecimal,SIZE bytes per integer 十六进制,每个整数占用SIZE bytes
SIZE is a number.For TYPE in doux,SIZE may also be C for sizeof(char),S for sizeof(short),I for sizeof(int),L for sizeof(long).
if TYPE is f ,SIZE may also be F for sizeof(float),D for sizeof(double) or L for sizeof(long double)
od -t c /usr/bin/passwd
以ASCII码显示/usr/bin/passwd的内容
cat /etc/issue
od -t oc /etc/issue
od -t oCc /etc/issue
观察'e',ASCII码对应的十进制是101,八进制145(1*8*8+4*8+5*1=101)
od -t oc issue
用八进制和ASCII码来显示issue
一行16个字节,od默认按int读取,int是按四个字节分割,所以上面分成了四段,
下面是按char读取,char是按一个字节分割,所以,上面和下面没有对齐。
od -t oCc issue
oC,按照char来截取,即按照一个字节来分割,这样上面和下面就能对齐了。
Linux文件有若干属性,包括:读(r)、写(w)、运行(x)权限、所有者(o)、所属组(g)、是文件(-)、是目录(d)还是连接文件(l)等等。
其中要改变 读写运行权限使用chmod,要改变所有者所属组使用chown chgrp。
chattr :change file attributes on a linux file system
使用root用户操作:
cp ~/.bahsrc /home/myuser/bashrc
ls -l /home/myuser/bashrc
-rw-r----- 1 root root 1177 Aug 24 11:56 /home/myuser/bashrc
su myuser
cd /home/myuser
ls -l bashrc
-rw-r----- 1 root root 1177 Aug 24 11:56 /home/myuser/bashrc
cat bashrc
cat :bashrc :Permission denied
su - root
chown myuser:mygroup /home/myuser/bashrc
su myuser
ls -l /home/myuser/bashrc
-rw-r----- 1 myuser mygroup 1177 Aug 24 11:56 /home/myuser/bashrc
cat /home/myuser/bashrc
可读取