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Actually, a typical invocation of sudo does not read the password from stdin at all. Instead, sudo will directly access the controlling terminal (a tty or pty, via the /dev/tty special file) and output the prompt and read characters directly. This can be seen in the tgetpass.c file in the sudo source.

There are a few other scenarios:

• If an askpass program is specified, e.g. in the -A param, that program will be invoked.
• Otherwise, if you specifically request sudo to read from stdin, e.g. with the -S flag -- and it will also write the prompt to stderr. This is the case where MadHatter's answer applies.
• Otherwise, if there is no tty available
• If password echo is disabled (it is by default, controlled by the visiblepw flag in sudoers), sudo will report an error: no tty present and no askpass program specified
• Otherwise, sudo will fall back to using stdin and stderr even if it was not specifically requested. MadHatter's answer will also apply here.

Actually, a typical invocation of sudo does not read the password from stdin at all. Instead, sudo will directly access the controlling terminal (a tty or pty, via the /dev/tty special file) and output the prompt and read characters directly. This can be seen in the tgetpass.c file in the sudo source.

There are a few other scenarios:

• If an askpass program is specified, e.g. in the -A param, that program will be invoked.
• Otherwise, if you specifically request sudo to read from stdin, e.g. with the -S flag -- and it will also write the prompt to stderr. This is the case where MadHatter's answer applies.
• Otherwise, if there is no tty available
• If password echo is disabled (it is by default, controlled by the visiblepw flag in sudoers), sudo will report an error: no tty present and no askpass program specified
• Otherwise, sudo will fall back to using stdin and stderr even if it was not specifically requested. MadHatter's answer will also apply here.

Actually, a typical invocation of sudo does not read the password from stdin at all. Instead, sudo will directly access the controlling terminal (a tty or pty, via the /dev/tty special file) and output the prompt and read characters directly. This can be seen in the tgetpass.c file in the sudo source.

There are a few other scenarios:

• If an askpass program is specified, e.g. in the -A param, that program will be invoked.
• Otherwise, if you specifically request sudo to read from stdin, e.g. with the -S flag -- and it will also write the prompt to stderr. This is the case where MadHatter's answer applies.
• Otherwise, if there is no tty available
• If password echo is disabled (it is by default, controlled by the visiblepw flag in sudoers), sudo will report an error: no tty present and no askpass program specified
• Otherwise, sudo will fall back to using stdin and stderr even if it was not specifically requested. MadHatter's answer will also apply here.

Actually, a typical invocation of sudo does not read the password from stdin at all. Instead, sudo will directly access the controlling terminal (a tty or pty, via the /dev/tty special file) and output the prompt and read characters directly. This can be seen in the tgetpass.c file in the sudo source.

There are a few other scenarios:

• If an askpass program is specified, e.g. in the -A param, that program will be invoked.
• Otherwise, if you specifically request sudo to read from stdin, e.g. with the -S flag -- and it will also write the prompt to stderr. This is the case where MadHatter's answer applies.
• Otherwise, if there is no tty available
• If password echo is disabled (it is by default, controlled by the visiblepw flag in sudoers), sudo will report an error: no tty present and no askpass program specified
• Otherwise, sudo will fall back to using stdin and stderr even if it was not specifically requested. MadHatter's answer will also apply here.

Actually, a typical invocation of sudo does not read the password from stdin at all. Instead, sudo will directly access the controlling terminal (a tty or pty, via the /dev/tty special file) and output the prompt and read characters directly. This can be seen in the tgetpass.c file in the sudo source.

There are a few other scenarios:

• If an askpass program is specified, e.g. in the -A param, that program will be invoked.
• Otherwise, if you specifically request sudo to read from stdin, e.g. with the -S flag -- and it will also write the prompt to stderr.
• Otherwise, if there is no tty available
• If password echo is disabled (it is by default, controlled by the visiblepw flag in sudoers), sudo will report an error: no tty present and no askpass program specified
• Otherwise, sudo will fall back to using stdin and stderr even if it was not specifically requested.

Actually, a typical invocation of sudo does not read the password from stdin at all. Instead, sudo will directly access the controlling terminal (a tty or pty, via the /dev/tty special file) and output the prompt and read characters directly. This can be seen in the tgetpass.c file in the sudo source.

There are a few other scenarios:

• If an askpass program is specified, e.g. in the -A param, that program will be invoked.
• Otherwise, if you specifically request sudo to read from stdin, e.g. with the -S flag -- and it will also write the prompt to stderr. This is the case where MadHatter's answer applies.
• Otherwise, if there is no tty available
• If password echo is disabled (it is by default, controlled by the visiblepw flag in sudoers), sudo will report an error: no tty present and no askpass program specified
• Otherwise, sudo will fall back to using stdin and stderr even if it was not specifically requested. MadHatter's answer will also apply here.