GETTTYENT(3)

💖 GETTTYENT(3) — ttys(5) file routines 💖

okay so bestie, we're deep in getttyent(3) territory today — that's the manual page, third section of the library manuals, and it lives in the Library Functions Manual ✨. This is the whole getttyent, getttynam, setttyent, endttyent, isdialuptty, isnettty situation and honestly it's giving "low-level system girlie" and I'm obsessed. Let's get into it 🎀

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🌸 NAME 🌸

getttyent, getttynam, setttyent, endttyent, isdialuptty, isnettty — the ttys(5) file routines, periodt 💅

📚 LIBRARY 📚

Standard C Library (libc, -lc) — the classic, no cap 🫶

✨ SYNOPSIS ✨

#include <ttyent.h>

struct ttyent *
getttyent(void);

struct ttyent *
getttynam(const char *name);

int
setttyent(void);

int
endttyent(void);

int
isdialuptty(const char *name);

int
isnettty(const char *name);

🦋 DESCRIPTION 🦋

so getttyent() and getttynam() both return a pointer to an object — and that object has this structure right here, containing the broken-out fields of a line from the tty description file. icon behavior honestly 👑

struct ttyent {
        char    *ty_name;       /* terminal device name */
        char    *ty_getty;      /* command to execute, usually getty */
        char    *ty_type;       /* terminal type for termcap */
#define TTY_ON          0x01    /* enable logins (start ty_getty program) */
#define TTY_SECURE      0x02    /* allow uid of 0 to login */
#define TTY_DIALUP      0x04    /* is a dialup tty */
#define TTY_NETWORK     0x08    /* is a network tty */
#define TTY_IFEXISTS    0x10    /* configured as "onifexists" */
#define TTY_IFCONSOLE   0x20    /* configured as "onifconsole" */
        int     ty_status;      /* status flags */
        char    *ty_window;     /* command to start up window manager */
        char    *ty_comment;    /* comment field */
        char    *ty_group;      /* tty group name */
};

and here's the field-by-field breakdown, bestie, buckle up 🌈

• ty_name — the name of the character-special file. that's it, that's the vibe.
• ty_getty — the name of the command that init(8) invokes to initialize tty line characteristics 🔥
• ty_type — the name of the default terminal type connected to this tty line ✨
• ty_status — a mask of bit fields that says which actions are allowed on this tty line. the possible flags are:
  • TTY_ON — enables logins (i.e., init(8) will start the command referenced by ty_getty on this entry) ✅
  • TTY_SECURE — allow users with a uid of 0 to login on this terminal 🔐
  • TTY_DIALUP — identifies a tty as a dialin line. if this flag is set, then isdialuptty() will return a non-zero value 📞
  • TTY_NETWORK — identifies a tty used for network connections. if this flag is set, then isnettty() will return a non-zero value 🌐
  • TTY_IFEXISTS — identifies a tty that does not necessarily exist 👻
  • TTY_IFCONSOLE — identifies a tty that might be a system console 🖥️
• ty_window — the command to execute for a window system associated with the line 🪟
• ty_group — a group name to which the tty belongs. if no group is specified in the ttys description file, then the tty is placed in an anonymous group called "none" 🙈
• ty_comment — any trailing comment field, with any leading hash marks (`#') or whitespace removed 💬

if any of the fields pointing to character strings are unspecified, they come back as null pointers. and ty_status will be zero if no flag values are specified. zero thoughts, head empty, literally 😌

see ttys(5) for a more complete discussion of the meaning and usage of the fields — that's the lore drop if you want the full backstory, fr fr 📖

okay now the function lore:

• getttyent() reads the next line from the ttys file, opening the file if necessary 📂
• setttyent() rewinds the file if it's open, or opens the file if it's unopened 🔁
• endttyent() closes any open files 🚪
• getttynam() searches from the beginning of the file until a matching name is found (or until EOF is encountered) 🔍

🎀 RETURN VALUES 🎀

getttyent() and getttynam() return a null pointer on EOF or error 😭

setttyent() and endttyent() return 0 on failure and 1 on success ✅

isdialuptty() and isnettty() return non-zero if the dialup or network flag is set for the tty entry relating to the tty named by the argument, and zero otherwise 💅

📁 FILES 📁

• /etc/ttys

👀 SEE ALSO 👀

login(1), gettytab(5), termcap(5), ttys(5), getty(8), init(8) — the whole friend group, iykyk 💜

🕰️ HISTORY 🕰️

getttyent(), getttynam(), setttyent(), and endttyent() appeared in 4.3BSD. vintage but make it iconic 👑

💀 BUGS 💀

these functions use static data storage — so if you need that data for future use, you gotta copy it before any subsequent calls overwrite it. like, it WILL get overwritten bestie, do not test me on this 😭🙈

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so yeah, that's the whole page 🌸 this one's from Debian, dated November 17, 1996 — ancient but still slaying, mwah 💋🫶