fork(), exec(), wait() and exit()

blog.koehntopp.info/2020/12/28…

This is an older blog article, a translation of an even older blog article in German, which explains the four main Unix system calls that deal with processes:

• fork() is the only syscall that makes more processes. It is entered once, but left twice.
• exit() is a syscall that terminates a process. It is entered once and never left.

Obviously, if the number of processes in a system is roughly stable over time, for each fork() there must be an exit().

The code running in a process is being replaced with exec().

A process can stop and wait for another process to end, using wait() or variants of it.

A good deal of the article is spent on the distinction of a program (code that lies around passively on media) and a process (code that is being executed, and has state, the state being the part that differentiates one instance of a program from another).

The last sample program is kind of the skeleton of a shell: It runs an external program in a fork()ed subprocess and checks the result. Add user input, redirection, globbing and so on, and you get a real shell.

writing-prompt-s:

Valhalla does not discriminate against the kind of fight you lost. Did you lose the battle with cancer? Maybe you died in a fist fight.

Even facing addiction. After taking a deep drink from his flagon, Odin slams his cup down and asks for the glorious tale of your demise!

Oh my god, this is beautiful.

A small child enters Valhalla. The battle they lost was "hiding from an alcoholic father." Odin sees the flinch when he slams the cup and refrains from doing it again. He hears the child's pain; no glorious battle this, but one of fear and wretched survival.

He invites the child to sit with him, offers the choicest mead and instructs his men to bring a sword and shield, a bow and arrow, of the very best materials and appropriate size. "Here," he says, "you will find no man who dares to harm you. But so you will know your own strength, and be happy all your days in Valhalla, I will teach you to use these weapons."

The sad day comes when another child enters the hall. Odin does not slam his cup; he simply beams with pride as the first child approaches the newcomer, and holds out her bow and quiver, and says "nobody here will hurt you.

Everyone will be so proud you did your best, and I'll teach you to use these, so you always know how strong you are."

A young man enters the hall. He hesitates when Odin asks his story, but at long last, it ekes out: skinheads after the Pride parade. His partner got into a building and called for help.

The police took a little longer than perhaps they really needed to, and two of those selfsame skinheads are in the hospital now with broken bones that need setting, but six against one is no fair match. The fear in his face is obvious: here, among men large enough to break him in two, will he face an eternity of torment for the man he left behind?

Odin rumbles with anger. Curses the low worms who brought this man to his table, and regales him with tales of Loki so to show him his own welcome. "A day will come, my friend, when you seek to be reunited, and so you shall," Odin tells him. "To request the aid of your comrades in battle is no shameful thing."

A woman in pink sits near the head of the table. She's very nearly skin and bones, and has no hair. This will not last; health returns in Valhalla, and joy, and light, and merrymaking.

But now her soul remembers the battle of her life, and it must heal.

Odin asks.

And asks again.

And the words pour out like poisoned water, things she couldn't tell her husband or children. The pain of chemotherapy. The agony of a mastectomy, the pain still deeper of "we found a tumor in your lymph nodes. I'm so sorry." And at last, the tortured question: what is left of her?

Odin raises his flagon high. "What is left of you, fair warrior queen, is a spirit bright as fire; a will as strong as any forged iron; a life as great as any sea. Your battle was hard-fought, and lost in the glory only such furor can bring, and now the pain and fight are behind you."

In the months to come, she becomes a scop of the hall-no demotion, but simple choice. She tells the stories of the great healers, Agnes and Tanya, who fought alongside her and thousands of others, who turn from no battle in the belief that one day, one day, the war may be won; the warriors Jessie and Mabel and Jeri and Monique, still battling on; the queens and soldiers and great women of yore.

The day comes when she calls a familiar name, and another small, scarred woman, eyes sunken and dark, limbs frail, curly black hair shaved close to her head, looks up and sees her across the hall. Odin descends from his throne, a tall and foaming goblet in his hands, and stuns the hall entire into silence as he kneels before the newcomer and holds up the goblet between her small dark hands and bids her to drink.

"All-Father!" the feasting multitudes cry.

"What brings great Odin, Spear-Shaker, Ancient One, Wand-Bearer, Teacher of Gods, to his knees for this lone waif?"

He waves them off with a hand.

"This woman, LaTeesha, Destroyer of Cancer, from whom the great tumors fly in fear, has fought that greatest battle," he says, his voice rolling across the hall. "She has fought not another body, but her own; traded blows not with other limbs but with her own flesh; has allowed herself to be pierced with needles and scored with knives, taken poison into her very veins to defeat this enemy, and at long last it is time for her to put her weapons down. Do you think for a moment this fight is less glorious for being in silence, her deeds the less for having been aided by others who provided her weapons? She has a place in this great hall; indeed, the highest place."

And the children perform feats of archery for the entertainment of all, and the women sing as the young man who still awaits his beloved plays a lute-which, after all, is not so different from the guitar he once used to break a man's face in that great final fight.

Valhalla is a place of joy, of glory, of great feasting and merrymaking.

And it is a place for the soul and mind to heal.

(Found on Instagram)